The feet are necessary if you are not going to bolt the lathe down. As Robo said having the lathe level front to back and across the lathe both front and back so there is not twist will help. You need the feet to level if you're not going to bolt it. I can tell you as a contractor that there isn't a perfectly flat concrete floor. Any slight little undulation can cause the lathe to become out of level or take a foot off the concrete even 1/32 of an inch can make a difference. Having said that more foot on the floor the better so bolting a lathe down IMO with a broader foot that is shimmed with steel shims, if necessary, offers you a lot of stability.