Every studio you walk into keeps their seamless paper backgrounds stored standing vertically. I never had the room to do that, so I stored mine horizontally. The reason you are SUPPOSED to store them vertically is to keep them in top shape.
If they sit horizontally for an extended period of time, the weight of the roll eventually starts to distort the circular shape. The roll looks less like a circle and more like a capital D. When you unroll it, your background looks a bit wavy. Not a big issue if you are using black and keeping it black, or if you are using white and throwing a ton of light at it. However, it can be very unflattering for colored rolls.
Well, I always figured that I go through my rolls fast enough that it didn’t matter too much either way. They wouldn’t really sit long enough to deform. Wrong! A couple of my specialty colors are starting to look very wavy. I am so stupid.
They only cost about $40 a piece, but still… why throw away money? I’m going to find the extra space somehow, and I’m going to store my backgrounds vertically from now on… like I am supposed to be doing.