If you do not commit any characters to the Quest what happens?

I assume the following:

-Encounter deck still reveals one cards per player.

-You did not put any Willpower towards the Quest so you increase your Threat by whatever the Threat rating is of the encounter cards in the Staging area.

This means you ALWAYS want to Quest every turn.  Which, based on the way things are written in the rulebook seems right.  But I thought I'd ask in case someone else found different in the rulebook.

Precisely, not committing to a quest at all would be a very bad idea.

So the guys you commit to questing can't attack OR defend, correct?

The best strategy would be just to throw the weakest attacker/defender with the most willpower right?

Otherwise, you won't have anything left to attack/defend right?

Typically, yes.  It's part of the resource management part of the game on what to do with your characters.  The leadership deck though, has a couple of ways to ready characters in the middle of the round.  So those characters could exhaust to quest, and if they're readied somehow, can also exhaust to block or attack during combat.  Aragorn is awesome for this.

Or better still, Aragorn + Theodred. Both commit to the quest, Aragorn readies again, and so long as Aragorn starts with 1 resource in his pool, there's no net cost!

Play lots of allies. That's how I've made sure that I can quest, defend and attack. At the moment I think allies are key.