I often find them prohibitive in terms of both space and cost. I tend to do cost/benefit analysis as far as buying them and keeping them. I only kept a handful of the big Mosaic sets in my collection as the music became available in other CD configurations(though I've kept a lot Selects). Yet things like the 90's Atlantic boxes on Trane, Ornette, and Mingus and the Prestige boxes on Trane, Rollins, Miles, and Dolphy, and the Milestone Joe Henderson box are perfect for my needs. I tend to work straight through a box set when I listen to it, regardless of size.