I have a slightly different opinion of line-by-line writing in writing workshops than most people seem to.
First off, I have to admit, that if I'm pressed for time, they're the first thing I will not look at when doing a critique for soeone else, and the last thing I will look at if I'm reading a critique someone else has done for me. That said...
I know that line-by-line changes in a first draft might end up being irrelevant, depending on how much rewriting the author does. And I know that there are bigger problems that usually be addressed. Even though, I think line-by-line changes are useful. Sure, maybe that piece of writing will get changed... But maybe it won't. And if it doesn't, one more pair of eyes to catch that extra comma or a poorly worded sentence are a help. And Jim Bob Joe over there might catch something like that in my manuscript that I didn't, 'cuz you know, I wrote the thing, so I knew what it meant.
The other reason I actually like the line-by-line edits is because it actually does help me get a feel for what's working and what isn't working stylistically, and that's the sort of thing I can keep in the back of my mind even as I'm writing the next chapter.
And really, even though it does add up when you're talking novels, the line-by-line edits are easy fixes. In the grand scheme of things, they just don't take that long to do.
Because there's a time limit with face-to-face workshop scenarios, I usually don't mention the line level stuff in verbal critiques. I'll just hand the author a marked-up manuscript after the fact. I've been basically doing the same thing here on the forums, keeping my crits broad on the discussion threads and emailing people back their manuscripts.
So, uhh... I guess the short version of that is I don't really think giving people line-level critiques is at all problematic (at least as long as they're getting adequate critiques about the bigger picture). Sorry for ranting. I am supposed to be writing an essay right now. At least this means I'm in the right mindset.