Unless your back-and-forth flew over my head, GP is referring to being able to format a range of lines in a file (i.e. a selection), they're not talking about selecting a formatting style.
Maybe formatting just the lines you've modified: on Emacs I'm a big fan of dtrt-indent, which fixes the indentation only on the lines you've modified, without breaking the style of the rest of the file. Great when collaborating on an open-source project. The default "format-on-save" setting would reformat the entire file, creating huge diffs for simple changes.
It's very handy for when you copy something in the editor and the file is not saved, you probably don't intend to save it, but you want to format the code, because it will be more readable.