There’s so much stuff I haven’t been aware of despite first playing the game in 1996 or so, and that location reveal thing is such a thing. It’d be nice if the game / UI signaled some of that stuff. It makes sense to have a time limit, balance-wise, but I don’t think the game tells this at any point.
I just spoiled myself from the wiki for a really funny-sounding strategy against psionic enemies: give your troops low-powered weapons (such as regular pistols and rifles) and put them in good armour. That way, if they’re taken over, they can’t hurt each other. Psi-aliens themselves are squishy, so they can be killed with bullets.
The interesting bit about this strategy is that the psi-aliens’ “companions” (that show up in terror missions and bases etc) are very well armoured..