It's called context / state.
The more state I can leave up on my desktop, the better.
If there were better management within the browser -- non-visible tabs were eventually unloaded, with any page-state (forms data, etc.) saved -- then you wouldn't have the memory bloat problems that occur.
The thing is that it's a very large virtual workspace to spread things out over. So long as it's organized, it's really useful.
Look to movies especially of researchers in the 1970s or 1980s who'd spread clippings and papers over all horizontal surfaces in an office, tape/pin them to a wall, etc. You want to be able to scan quickly through the space at eye-speed, not have to dig into files / organizers / storage / regenerate the information every time you want to look at it.
It's why you'd rather have a large monitor -- you can strew windows over it and see more, rather than have to manage windows and go through them repeatedly.