I went round the houses on this a little while back. My little Dremel makes a heck of a mess trimming pots down and I was always concerned about swarf getting in the pots, as well as any impacts from the vibration and the heat. Plus it took ages, but that may just be my dodgy old drill!
In the end I'm finding that a pair of anvil secateurs is perfect for plastic shafts, very neat and controllable and takes no time at all. Snip - done. For metal shafts, I use bolt cutters - same principle, though you have to be careful as the snipped-off end will go flying like a bullet! Tape helps. But I generally avoid metal shafts unless there's no alternative, as plastic is so easy with the secateurs.
It's worth noting that bolt cutters will make a screaming mess of your knurled split shaft.
Andy