For me, open tabs and bookmarks are different levels of the same thing. I'll open a bunch of tabs researching some task I want to do, and leave them open because I want to come back to that. Bookmarks do the same thing, but with lower visibility and higher permanence.

Tab groups let me group a handful of things to reduce the clutter. Similar to the way that folders are useful within the bookmarks manager.

To use them, just drag one tab on top of another, it'll make a new group. Give it a name, and you can now expand/collapse. So 10 tabs all related to one task can stay in-sight to remind you, but only take up 1 tab's worth of space in the bar.