Its only polite to go outside to use your glimmer mists when you're cropping in someone else's space. Its also time consuming (I usually leave the builing and mist on grass, etc.). This let me use my glimmer mists at my spot without having to worry about staining.
It lasts a long time, actually dries fast without a drippy mess, doesn't get mushy like a regular cardboard box, takes up little space, can be easily packed. Is it a necessity--no. But I was constantly cleaning up spray from my table and and going through cardboard. And for $3.50-5.00 (depending on whether you use a sale or coupon to buy it), I highly recommend it. I use my mists much more now--easy to set up, no clean up required.