What is the use of a spray box?

I use document boxes - they are basically the same construction as pizza boxes, but 12x12. I use them for shipping cookies and took a couple of spares out for myself.

Never thought to take to crops - that's a great idea!!

I used to use a box for spraying, but I am so limited on space, I had to come up with something else. So I just use plastic grocery bags, lay it down, spread it flat and then "poof" it up and place my piece inside and spray away, never gets on anything else and easy to grab another if I don't want colors to mix, cost me nothing, easy to store and somewhat recycling.
Works for me.

For color & shimmer mists, I don't use a box, I just put down my non-stick mats and sometimes a couple pieces of cardstock reserved for this purpose (they're stiff and shiny and colorful with all the spray they've taken on so far!).

For spray adhesive I have one of those big plastic bags that comforters come in, I keep it as closed as possible, zip it closed as much as possible and holding the 'lid' with my free hand, while still keepig it usable. Since it's an aerosol it literally does go EVERYWHERE (unlike color mists which are just a squirt) so I do what I can to contain it. I just put in a clean piece of scratch paper when the last one gets too sticky, so whatever I'm spraying doesn't get stuck to the bag.

I use an empty box from the grocery store, cut out one side. It works for me when spraying inks and spray adhesives. I just put a clean sheet of copy paper down every now and then when it gets too messy or sticky. I keep it under my work table.

Here's a simple one:

That would make sense. I don't go to crops, so mine sits abandoned

If it's an official one then it's a great way to take a box to a crop (because it folds up) so that you can spray something without making a huge mess. I've had one for a couple of years and it's been pretty handy!

I just use the top of a box. Or like others said you could just use a box that you received something in.

I bought a folding spray box at Mike's, but always forget to use it. If I'm going to make a big mess, I take it outside to spray. Usually I make sure the overhead fan is off, then just spray, but I haven't done much color spraying. Then I'll just use a big box. (Anyone want to buy an unused folding spray box? :>) It will probably end out being kindling for a fire at the beach.)

ditto what's been said. I'd recommend just using a large box from items you've had shipped. I bought a "spray box" that is a collapsible/folding one, but it's really not big enough, I still get ink all over the place!

Misting would be my guess so the spray doesn't get all over the place.

Not really 100% sure what you mean, but maybe you're thinking of a box that people spray items in? As in, you can put some cardstock in a box and spray it with color mists - the box keeps the mist from getting everywhere.

What is the use of a spray box?