You absolutely can, but with the tool it's no more than a couple of minutes per bush instead of cutting and drilling and swearing for ages each time.

When I fitted Powerflex bushes to the front thrust arms I cut the old ones, that wasn't too bad, but the rear subframe bushes are much larger and will take correspondingly longer to cut. There's four of them and access is not so good at the back either.

So not essential, no, but it saves quite a bit of time & hassle.