On vBulletin, there's the default Subscriptions folder, but you also have the ability to create custom folders. For example, Special Subscriptions.
A while ago I started removing watched threads (XenForo) / unsubscribing from threads (vBulletin) at the beginning of the month that were from the previous month just as a cleanup and to keep things organized. However, there are certain threads, such as special project threads I work on, that I have. On vBulletin forums I visit, I've created a folder called Special Subscriptions where I put those.
It would be nice if an option to create folders for your watched threads were added to XenForo.