For me its a linear view of how I got somewhere when I'm doing exploratory research. Usually a tree of tabs (I use side tabs) will start with a google search, then go to a site, then another site, then another. When I find something interesting and think "how did I get here again?" and I can just glance at my open tabs.

This context is useful if I get sidetracked/distracted by a coworker, so I can retrace why I was looking at a certain page.