Don't stress about it. There's really no reason to drive with a putter other than to just do it.
No. If you have no ceiling, a putter will finish straighter than most discs. Accuracy is sometimes (read: usually) more important than distance.
The advantage I see is that it improves your form and knowledge of your equipment.
No. It improves your putter-driving form and knowledge of your putters.
But in an actual playing situation there's no reason to do it. That's what mids are for.
Mids are for low ceilings on short drives, or for longer open distances than your putters can reach.
And Ive seen tons of "putter driving" videos that claim 300 feet and I highly dispute they get past 250 just on flight time alone. I can get my trim Ridge and my Graboide out to about 220 Max and my XG Rhyno out to 180. But its not an essential skill...like I said its more to gain knowledge of yourself and your discs. If you're learning just one thing, you're doing everything right.
My best distance with a Pro Rhyno is 250'. I drove Hole C shorts at Hudson Mills Monster during a tournament, went dead straight and landed 20' behind the pin. The basket is tucked in to the left.
My point? My best drive EVER is about 350', but I can get a putter out to 250'. Just because you can't get yours past 220' doesn't mean it can't be done.