when uploading through brower and it stops half way on large folder
or when you have worked locally and now need these new files to be added to online
or when you have a backup but maybe dropbox folder was from a more active copy and might have more files
or just to validate equality of contents and validity of copy/upload
especially when not using sync (for example I cannot use sync because I have over 70TB on dropbox and just indexing when starting up takes days if it completes at all) so I generally upload through website a small folder like under 50GB (since im told that's the limit in browser)
anyway I use Visual Differ all the time. At the least should be able to have an option in the dropdown in browser to show meta data and properties. there's a way to show size but doesnt show long form byte count to verify a copy or items contained count like a finder in OS does. but to go one step further with a visual differ type of functionality would be really idea. you drag both folders in to a comparison window and then it analyzes and shows side by side the items, any differences and you can sync or copy from one side to the other or both ways to make any differences be resolved and so the backup is up to date without having to delete a backup and reupload the whole folder and sometimes a backup might have some items the active does not.