When you come across a single website you want to send to a friend, that's easy to do. If you have a bunch of sites open and you want to share them all, things get a little more complex. Tabulate expedites the process of sending many URLs by taking all the open tabs in a given window and providing you with a single short URL that links to them all.You can then send that short URL to someone, who will be presented with all your links. It's a one-click solution for something that would normally take a little time to accomplish.
Tabulate is also useful if you just want to save a bunch of tabs for later and quickly close them out. Personally, I visit far too many web pages per day and leave a lot open I want to look at later. While there are definitely other services for marking stuff for later reading, Tabulate lets me put together URL collections of a particular category very easily. I can create a quick multi-site short URL of research I'm doing on a particular topic, for example. While it won't be for everybody, it's a really great extension if you keep a lot of tabs open for too long or want to easily send large amounts of content to someone else.