EDIT: It is also worth mentioning that undermining gets you a quick 30 Powerplay Vouchers for each ship you take out! As opposed to the measly 1 PP Voucher from preparation, expansion or, fortification. Although that may just be the soft, kind hearted, “Love thy Federal Neighbor” me speaking.
Also worth mentioning, that if you’re winged, everyone who gets a shot on the target, gets 30 points each.
Which all count to the undermining of the system, and all count to your PP points. So a wing of 4 in a system for a couple of hours can do some real damage to a system.