On a semi-custom build I'm working on, I have the standard rolled ball screw with fixed bearing block setup in the standard Y arrangement. The ball screw is securely fixed on one end and floating on the other. The Nut is secured to the platform which is in turn aligned by the ways/gibbs along the track. You're all probably familiar.

So this machine has a burly steel plate on the end. When it was previously an acme thread it had a bushing in there on the floating end. Now that the ball screw is there and I've rearranged some things, I have to make something else. But as the rest seems to be right the screw is already constrained by the fixed end and nut & corresponding surfaces. Turning this screw results in a floating end that is pretty near perfectly concentric even if it's literally floating in air unconstrained (as one would hope). I now plan to make either a brass or teflon bushing to put into this steel plate and constrain it anyway- but the more I think about it the more I wonder "does it even matter?"

Interested to hear opinions. Thanks!