[bluGill]

When I intentionally want to read something that is what I do. However once in a while I'm scrolling, selecting a window, or some other activity; and I happen to click on a link: instead of whatever action I intended I end up on a new page I didn't want to read (maybe I will want to read it, but I haven't go far enough cognitively to realize that). That is when I want my back button to work - a get out of here back to where I was.

[docmars]

Exactly, it has the potential to make you lose something important, forcing you to dig through browser history to find it again. If it happens to be a long-lived tab, you might be searching for a while if you forgot the name or site you were on.