The charges are pretty useless. I think they're in only because the original JK engine (IM is made with it) supported that kind of weapon.
The satchels tick for a short duration of time, or go off earlier if Indy or a Russky steps on them.
I recall using them in only one point, there was a tunnel you needed to blow open by shooting at barrels in level 13 (King Sol's Mines)... I used a charge since the room was so narrow Indy always took a little damage if I blasted the barrels with a gun.
The function use the things as mines is really bad, since they go off after such short duration and besides the enemy AI is so unpredictable you can never even know if they come after you after you've deployed a mine on their assumed route.
There could have been more use to them, though. It would for example have been cool if you had managed to blow open those walls you usually used Urgon's part with.
