Tnx, Cathy -- that's exactly what I was about to add.

Underlines are at the very least a courtesy for the proofreader. Previously, they were a necessity for the typesetter. (And, of course, it wasn't all so long ago that we were still all using typewriters -- it ain't fun to type actual italics, even with a Selectric.)

If you have ever printed out a page that's had skewed text, then it won't take you a second's thought to realise why underlining is helpful.

Don't tell me about electronic files. I've edited submissions where the writer had trusted the software too much, & stuff s/he'd changed had unintended consequences, inserting different chunks in the middle of a phrase, so that I'd see stuff like interesting, which doesn't exactly jump out during edit.

And, finally, if a new writer were forced to look at page after eye-killing page of underlining, s/he might get the idea that maybe s/he's using entirely too freakin' much artificial emphasis.