When I bought my Tormach CNC, I added the 4th axis (a steeper driven RT). I hadn't a specific use for it but wanted to expand my capabilities. That was twelve years ago and I believe that I have used it once.. To be fair, I have a 12" RT which is semi-permanently mounted on my RF30 clone.
Both a steady rest and a follower rest came with my Grizzly G0602 some seven years ago and neither has been used. The right project hasn't come along yet. My faceplate is used for checking headstock alignment rather than the more typical use. If I had a set of lathe dogs, I might be more inclined to use it though.
I have a sine plate that has been used once or twice in the past five years and a 5C collet fixture that has been used once. I'm sure if I took an inventory, I could come up with other examples.
For me at least, how often a tool gets used depends in part on how easily it is set up. My 12" RT has a semi-permanent place on the mill because it is too heavy to install and remove without very good reason. I find it useful at times and because I have a second mill, I am content to leave it in place. The 4th axis RT is also bothersome to install and remove but it takes up too much real estate to leave on permanently so it sits in the cabinet under the mill. I used to avoid single point threading because of the bother of messing with change gears. Likewise, using power feed required messing with the gears so I would tend not to use it. Now that I have an ELS, setup for threading or power feed involves flipping a switch and pushing a few buttons so I use them much more frequently.
Although I haven't used the above mentioned items very much, if at all,I still wouldn't want to part with them. Almost certainly if one of them went out the door, I would have a project that could not be completed without it.
edited to include missing "not"