It depends on the context, if you ask me.
If you're playing to improve, then yeah, it's not worth your time. You'd be better off fighting somebody that's going to help you by putting up a real challenge. Even so, it can be rewarding in its own way to fight a staller: it's good experience for something that's not uncommon in tournaments.
If it's in a tournament and they don't even want to win, well hey, free victory for me. If they're just trying to lame me out, then they're probably playing to the clock and trying to time me out, in which case I can't really begrudge them. It's a legitimate, if irritating, strategy. Just makes me want to beat them even more.