A couple I have used for storage of other things like watch straps there are one or two that are "travel cases" so are practical to keep. I think of some watch boxes I have had over the years, I bought an old Omega years ago with box and papers the box was literally disintegrating, parts of it stuck to the outer card looking back I now think "what is really the point of keeping it?" I suppose like everyone else the whole selling with box and papers is always what a buyer is after.
I wonder where that first came from? Perhaps from back in the day when people only had one or two watches and sold on to dealers so popping into a shop having the original box was a bit more "proof" of ownership rather than buying it off the bloke down the pub? These days though it really offers nothing to the providence of the watch. I read here somewhere Rolex back in the day suggesting using the box as somewhere to store your cigarettes!
I am a bit like that with watch straps though, never really understood the point of wanting a second hand watch with the strap, unless its a bracelet I tend to suggest taking the strap off and keeping it unless its say with the original buckle.
Someone mentioned Citizen, from memory I think they had boxes that could reasonably be re-used as something else? Seiko seem to be mostly boxes made to be disposed of.