I put mine on comic boards and I got three times the amount of fabric in my cupboard that I previously had. Its so easy to pull out check a color then slide back in. If you use the foam boards instead it does take more room. The comic boards are just heavy card stock so not very thick at all. my shelves were stuffed with ruler folded fabric but after I put it on the boards I was able to unload another two 17 gal tubs of fabric and put that on boards and put that in.
My sister who has been quilting for 35 years after browsing my shelves has asked me to help her put her shelves of fabric onto the boards as she is tired of shifting the stacks to find what she wants. It can be a personal choice and your shelves can make a difference. Mine are just the right depth and shelf height to fit the fabric on the boards. I love mine but use what works for you I bought 100 to start and now am up to almost 500 fabrics on boards and still working.