Have this folder as well but no idea what it's for.
My only guess is that it's to do with the boost c++ library, which doesn't automatically make it suspicious, but it does concern me that only some wallets seem to use it.
I did a full sweep and nothing came up. Various google searches haven't been too clear either.
I did find that some wallets use a boost::interprocess code or something, I'll check some of the older coins as well to see if it shows up there as well.
Looks to be something that is used for syncing the wallet, but better safe than sorry.