What is the practical usage of concealed squads? To move closer to the enemy? But the concealed squad is revealed as soon as it moves into LOS. The opportunity of hiding in buildings and woods?  Any  other ideas?

San said:

Small detail: A concealed squad within LOS but in cover-providing terrain, remains concealed ... and can't be fired upon. Just think of the nasty things you can do with that ...

Latro said:

I use the transport token on the board instead of using units (camouflage symbol face up and number face down). Off-board I identify my units using de correspondent transport token (retangular).

That's about it other than firing Anti-tank weapons as well.  Since it's the equipment attacking the enemy unit and not the squad you don't reveal the squad.

San said:

... a concealed squad can choose to become active and show itself by attacking anytime you want it to. Combine that with the fact that a lot of scenario's are decided by controling locations on the map within a certain time-limit and concealed squads can become a very dominating force if played correctly.

I have also found that concealed squads in cover slow down an enemies advance as the enemy has to close with the concealed squad but the concealed squad can attack them before they have a chance too most of the time