They certainly aren’t necessary.
But I’m using them. They do make rearranging easier, and I don’t like the idea of drilling and getting sawdust in my system. Though evidently Sam doesn’t drill, just puts screws in directly, but that doesn’t appeal to me either.
The Performance Filter has non standard hole spacings, so that could be problematic with rails. (You probably could drill new holes in the panel.) Other modules both from LMNC and other people seem to be pretty well standardized.
One other potential pitfall is if you make your own front panels from cut-to-order aluminum, typical tolerances in the US are -0 +1/8", so your panels could be as much as 1/8" too tall. That’s a problem if you use rails with lips like Gie-Tec or TipTop. Less so with Vector rails at least if you allow some slop spacing between one row and the next.