Not everyone's memory works the same way, and not everyone's organizational skills are the same. Whereas (it sounds like) you remember a task you're trying to do, and then go do it, and make a new tab and go do the task, for others, coming across the tab itself serves as the reminder about the task, and a call to action to do it. I'll open a tab that I need to do X, forget about X/procrastinate about X, open a tab for Y, and then Z, and then through going to a random tab, get to the tab about X, get reminded about doing X, and then go do it.

Sure It can. For example, If I'm looking for a certain stackoverflow post about a project I'm working on, I know it's be on the window with the other resources for that project, and I can remember that it's roughly on the middle right portion of that group of tabs. That narrows it down to <10 tabs to quickly check.

If I use my browser history, I'm going to have to re-filter out all of the webpages I deemed inadequate. If the tab was left open, I know it was at least somewhat useful.

Firefox switch to tab, my friend. You open a new tab, start typing the title of the page or the address of the site and it shows up in autocomplete with a switch to tab indicator and when selected it moves you to that tab instead of opening a copy.

An activity log and a to-do list are two very different things. Most of the things in my history I don't want to come back to.