A couple of companies ago I was the lead developer working mostly with people who were early on in their careers, single, and wanting to put in a lot of time.

A couple of companies ago I was the lead developer working mostly with people who were early on in their careers, single, and wanting to put in a lot of time. Even then I always advised them that programming and solving problems is fun, but they should find side projects or something and not spend all that extra effort on work projects. Even if they start doing it because of passion it can ruin things at work because it gives the managers a very poor sense of scale and estimation (because it's hard enough to estimate when you don't have to think about how interesting a given developer will find a problem as part of calculating velocity), it sets expectations on them that they really don't want to have (people start to count on your long hours even if you suddenly have something else going on in your life) and finally fresh ideas and new perspectives are the lifeblood of a team, so having people doing their own thing outside of work and bringing in those things is way more valuable than getting that one project done a little early.