I know that there was a couple of APCs in ArmA 2 that had interiors.
They were the M6 Linebacker, and the BTR-60, but I don't know if there were others,
I like looking around the interior, peeking out small windows beside and in front of me, instead of just having a 2D window to peek out of.
Kind of like the tanks in Red Orchestra 2, where you can look around the tank interior.
It would add a LOT of immersion, and as a soon-to-be armoured soldier, it would be much better.