I think the biggest risk with the people who work their asses off more than they should (doesn't matter if it's good or bad code) is that they end up with a non-sustainable output. Productivity is artificially high, and often achieved by overtime, working weekends, and overworking themselves. Eventually that leads to burnout, lower quality, and it becomes hard to replace. When it's people working too much and delivering bad code it's probably not as bad, though.

At my current company we have someone in this situation, with work affecting their day-to-day stress levels very much, to the point of damaging their personal relationships. Their manager is young and inexperienced, and doesn't see the issue, but he was flagged by HR and I hope something gets done.