Learned the hard way that while you can grab invisible or camouflaged units with a Blitzcrank Q, Rocket Grab, it will only make them shimmer when it hits them. By the time they are sitting in your lap they will be invisible or camouflaged again and therefore untargetable by Power Fist since it is a targeted ability. You can damage them and silence them with Static Field, so you need to be able to kill them outright with Static Field or with some AoE follow-up from your teammates to take full advantage of the grab.

If you have a Refillable Potion or Hunter's Potion or a Corrupting Potion and you want to get back to lane faster you can spam whatever charges you have left to heal up faster while standing on the fountain. The charges will refresh.

You can also do this with a Health Potion or a Total Biscuit of Rejuvenation if you want to get back to lane pronto, but you can also sell those for some cash back so choose wisely.