My level doubled as a string line today and it was a game changer.
I was working on a small wall by myself and didn't have a string line. Using my level to keep things straight worked great. Idk, maybe it's just me, but it helped a ton.
That point about tile and shelving is good, but a level isn't always the best swap for a string line. For example, on longer runs, a level can drift if the floor isn't flat (which it often isn't). With tile, you need a line that goes all the way, and a level's short length might let errors build up. For shelving, if the wall is out of plumb, using just a level could give you crooked shelves. It's a clever hack for small jobs, but for anything bigger than a few feet, a real string line is way more reliable.
For a 12-foot tile floor, I relied on a long level and had no issues. You can snap chalk lines based on level readings to guide the whole run. Checking every few feet with the level catches any floor unevenness before it compounds. String lines can sag or get bumped, but a level gives a solid reference each time.