The first thing I do when I work in an editor with a mini-map is -- turn it off. I find it mostly the most useless feature for coding, and for sites it seems to be equally useless. Why? 1. Stuff is too small to really make out where I'm going or navigating. 2. Short or long pages, both don't really benefit from the loss of screen real-estate. Or the distraction really. 3. Other tools like a proper index with descript…
But I think of code very visually and spatially and I don't split files until I have to, so it does help me quickly navigate to be able to sort of see the "shape" of a file and to be able to quickly jump around in it, especially if the file is divided into clear sections. Mostly just personal preference, and I agree they should never be mandatory.
And agreed on the large images/maps, most image editors have a viewport feature like that and it's pretty useful when doing detail work.