I think it depends on what you do. I'm contracted to work 40 hours, but the contract includes a clause about "and extra hours as required by the business."
I will work longer if in the middle of fixing a problem (we also have on-call, which is rota-ed.) I have been working longer to spend time on a project I have volunteered for, as it is something I'm interested in, and will be good for my career longer term. But as a general rule, I think it should be avoided. Also, if I sometimes work a bit longer, I can get flexibility for the times when I need to come in a bit late because I've been to the dentist or something, so to a certain extent it's mutually beneficial.
I'm in a department of 40; if each of us did an extra hour a day, that's a whole week's work for one person. We're a support department, and sometimes we do need to work a bit more to fix a problem. But if everyone's doing it regularly, then it's actually covering up the fact that there's more than enough work to support more people (not that we'd get the budget for to take on more.)
Also, I grew up on a farm, and if the weather's with you in summer, you do the work needed to get the harvest in. Cows have to be milked, and sometimes need help calving. Water problems need fixing so livestock don't go thirsty. Gaps in hedges need fixing. You can't just stop because you've done your hours in some cases, not if it's going to cause suffering to animals or people who can't fix it themselves.