One of the things you'll notice if you ever play hall pong is that ping pong balls will break, and fairly easily, too. (Especially the tournament quality 3-star balls) The logical way to get around that is of course to use harder balls, like whiffle-style practice golf balls. They're made of much tougher plastic, so you can use just one for a long time.
But using a different ball also changes the dynamics of the game significantly. For one thing, they're more massive, so they don't slow down as much while flying. A hall pong court is just long enough that you can hit a ping pong ball from one end to the other and have it arrive at a reasonably slow speed, but these practice golf balls can seem to come at you like bullets. It makes defense a lot harder and really tests your reflexes.
The other thing about the heavier balls is that they don't seem to bounce as well. Or rather, they bounce and keep going just about as fast as they were going before. So on defense, you'll have a tendency to be jabbing your paddle at the ground a lot, increasing the risk of breaking it. Of course, the sport of hall pong is no stranger to breaking equipment, but paddles are a little more expensive than balls and it'd be nice to keep them around. If you want to play this faster variant with practice golf balls, I'd recommend investing in some extra-sturdy plastic ping-pong paddles so you don't have to keep replacing them.