@EA_Blueberry As others have said, fairly common in breakthrough (and frankly, very effective) for dealing with vehicle snipers or infantry blobs.
I haven't seen it much in conquest, though i think that's due to the speed of the drone and the amount of terrain to cover/drone going out of range, easier to deploy effectively with a bottlenecked map and lots of troop concentrations.
If a vehicle is moving it's a lot harder unless you have people working in pairs with comms (one flying the drone, one placing and detonating the C5).
With the guy flying calling the detonation without needing to disconnect from the drone/pull out the detonator, it's a pretty evil combo.
In the case of the latter it's obviously effective against just about anything that can't move faster than the drone, you've essentially got a tow on steroids you can fire from complete safety of cover with no uncontrolled forward momentum to worry about.