I know what it does, but I've been wondering what stats are the best for it to work on.
I've realized these ones thus far
Weapon & ballistic skill(obvious reason)
Perception(with psyniscience and in some cases awareness for detecting stuff)
Strength (when grappling)
Willpower(when resisting psychic powers with opposed test)

My question is: Is there a reason not to always put it on WS or BS? They are the only ones that are quite actively used, and looking all others, the uses are really situational, and even in case of perception, the psyniscience is not going to happen unless you become into a psyker, which is, as far as I understand, a really really really rare case. Willpower is situational too, which requires A: enemy to be psyker, and B: enemy psykers to use opposed WP tests.

So in short: Is there any other stats(or the ones I pointed) for renegade to pick on, and have uses that I didn't notice?

I've seen it used by three different players to create snipers, due to how the Accurate trait does extra damage based on DoS. Sad, really, but that's what it's best for.

If you are going to break from renegade's fighting style, you can become psyker and get it to willpower, get some fellowsip skills and get it to fellowship or get it to int for a lot of skills where DoS may matter. However even though you'd get one more DoS, standard psyker/demagoge/heretek gets +5 to that stat so it's like +0,5 DoS for you.

WS/BS/Agi seem to give you the most because of multiple attacks/dodges and also because you can switch one damage die with your DoS.
 

switch one damage die? could you elaborate please? 

BC book, page 241 (damn, that was hard to find);

"STEP FOUR: ATTACKER
DETERMINES DAMAGE
After the hit location has been determined, the attacker
determines the Damage dealt by his attack. Each weapon has
a Damage listing, which is usually a die roll, plus or minus
a number. Roll the appropriate die and apply any indicated
modifiers. Finally, if the attack involved a melee weapon, add
the attacker’s Strength Bonus. The result is the Damage total.

For all attack rolls, count the Degrees of Success. The attacker
may choose to replace the result on a single Damage die with
the number of Degrees of Success from his attack roll. If the
attack inflicts more than one die of Damage, the attacker may
replace the result on one die of his choice with the Degrees
of Success from the attack roll.

If a natural 10 is rolled on any
Damage die, there is a chance of Zealous Hatred""

Continuation question: how does that function in semi and full auto weapons? (or swift and lightning attack modes) 

As I understand it, you can choose which one you replace. Same with weapons that roll multiple damage dies.

So in short: Is there any other stats(or the ones I pointed) for renegade to pick on, and have uses that I didn't notice?

Counter-question: Is there any stat that doesn't have a use for some more DoS?

Sure, if you're in a combat-heavy game, BS/WS is the way to go. However, the Renegade is pretty much the only archetype with a large sneaky potential - get Adroit Agility for every opposed stealth test. You could also make a more combat-ready apostate by going Fellowship. Perception might be helpful for a watcher-type who doesn't let things escape his notice.

Toughness and Willpower are pretty much the only abilities I wouldn't choose because those tests are generally just Save or Sorry, with not bonuses for exceeding the target.

Cifer said:

If you're running a Tzeentchian Renegade (and thus are likely to get Psychic powers, as you get PR1 from being Marked), Willpower may be useful (as Degrees of Success on WP Tests are useful to Psykers), but that's an edge case.

@N0-1

Of course. Once a few more books are out, I guess there'll be some kind of heretic who can benefit from Adroit Toughness as well.

 Honestly for a sniper type character I'd be more likely to pick Agility as opposed to BS.

Given you're only firing single shots, the benefit is fairly limited (Replacing DoS, helping get the accurate bonus). Although this is important, it'd be more important to remain undetected by your opponent given that as soon as they're aware, you're going to have a hard time dealing with them simply dodging your attacks.

@ Cifer

As I've stated in the starting post, I've pointed out all the uses I could think of, and for me they seemed pretty situational. You're not always able to stealth, you're not always the person who gets the awareness check(and I think it only matters here for vs stealth checks?), and heck you're not going to be a psyker anytime soon, if ever.

@PnPGamer

You're not always going to be able to shoot something either. Everything is situational. That being said, when you're mostly working undercover on imperial worlds, having agility for hiding or perception for knowing when to hide (note that Scrutiny is dependent on Perception as well - "Yeah, I'd like to join your cult and I'm totally not an inquisitorial acolyte!") would certainly be more useful than being able to take one more guardsman with you when your hideout gets overwhelmed. In a hack-and-slash game, BS and WS trump everything. In a more cloak-and-dagger setting, I'd rather have one of the characteristics that don't blow my cover half the time they're used.

As for "not always being able to stealth", we're talking about Chaos here. 80% of the time, you should be the ones acting, meaning you get to dictate the rules of engagement.

 I think the most useful and least situational is agility.short of psy stuff agility will keep you alive in the most situations. Id like to have a re roll when im determning the fate of my charicter. No body likes to get hit with a semi truck or a power fist in cc or even a las cannon blast. Agility will keep you alive in the most situations thats were i put my re roll and ive came out alive in quite a few situations.

 I had a renegade in a game I ran and he was going for a sniper so he took BS. However if I was making a renegade I'd more than likely pick fellowship, it could really help you be good at stuff other than combat which the amount of is going to vary between games and certainly I would consider WS or BS when taking a renegade into some GMs campaigns. Entire sessions can sometimes be purely combat or some sessions can have not a single combat roll asked for which leads to the appeal of fellowship for me, pick up a few social skills at trained and you can not only contribute but you can be damn good at the social encounters.

 Question: if a Renegade barely fails a test with their chosen characteristic… could the special ability make it a success?