How many times do you actually make it to your destination without the vehicle being destroyed? Likewise how often do you get in un-noticed by the ops? Chances are you'd be too preoccupied with placing your beacon/charges to know when anyone was near or in your ride.

The idea of having a passenger is better: not only is your ride safe from capture, you have someone watching your tail, and if you're quick/lucky, you could swap and double the C4 on the MCT. Thinking about it, if, say, your hummer is blocking the building doors and the ops can't kill it quick enough (i.e. occupied by a passenger) they might opt to go around the other side, in which time your charges should have gone off

Just another side of the $0.02 coin!