For the things I do, I use the 3' ones most. I have 2 pairs of the 3' ones and 1 pair of the 2' and 4'. I've never had a problem using the 4' ones on shorter material but I've never tried using them on things shorter than 3'. I could see it being clumsy and awkward trying to use longer cauls on material considerably shorter than the caul.
One trick to make installation and removal easier, if I have access and can put a clamp in the middle, that is where I put the first clamp to hold the caul and then one on each end. At removal, remove the end ones first and the middle last. The middle clamp isn't needed but makes things easier especially on the longer ones.
I only ever use one caul on the one edge that I'm gluing but if you aren't careful, that can be a problem if what you are gluing isn't big enough to resist the tension of the caul. You could glue an arc into whatever you are clamping and may need to use a caul on both sides.