Another filter question?

Just wondering when you buy a filter other the UV do you buy that filter for that len or do you buy it so it can be used with a step up ring and another or 2 lens
example i recently bought a Hoya R72 58mm so i can use it with my G2 with a stepup ring also with my 50mm 1.8 with stepupring and my 75-300.

I prefer to have enough filters to have one mounted on each lens simultaneously--but I only use filters at all when necessary for conditions.

I put a 58mm step-up ring on my 50mm f1/8 to match the filter size of my 24mm F2.8--that was to reduce the number of different sized filters I have to deal with.