Ranked in these QuestionsQuestion Ranking
Pro Way easier to manage large amounts of tabs
You can get up to about 2000 tabs per profile, though you start running into some issues after about 1000 tabs. How much RAM is available seems to be the main limitation. It's also easy to create tab groups and to move tabs between them.
The person who did the original version stopped work on it and is presumed dead in the Fukushima disaster. A group came together to redo this extension and get it to work on newer versions of Firefox.
Pro Tabgroups can be exported
You can export a tabgroup and drag/drop it into another profile to copy a tabgroup elsewhere.
Con Higher memory usage
Having a large number of tabs is going to raise memory usage.