I view bookmarks as being for sites that I intend to visit regularly enough to warrant making a handy link. A tab is for a place I plan to visit once, probably soon, but not right now, so I want to remember it, but not to the point where I'll make a dedicated bookmark link to it. Usually it's a video I want to watch at some point when I have more time, or a recipe I think I'll try making in a few days. The issue is when I don't get the motivation to do what I kept the tab open to do, so I start getting a backlog of tabs that I simultaneously don't want to lose because I kept them open for a reason, but I don't want to visit because there are too many of them to parse through.