It's a bank account. If I notice the company often needs bursts of work, I'll leave a little early every day so that I have reserve funds to pitch in extra time when needed. If I'm working 40 hour weeks already, there's nothing left in the account.
When you're young and without responsibilities, there is no glaring cost to giving away free labor, but if I do so, it comes directly out of my time with my kids.
I just think it has to go both ways. I don't want my boss coming to me with a problem because I worked 7h 58m one day. On the flip side, I'm not going to send him a bill or count the minutes if I stay a few minutes late a different day.
I said it in another comment but it's being unflinchingly rigid that I think in a problem (in either direction).
When you're young and without responsibilities, there is no glaring cost to giving away free labor, but if I do so, it comes directly out of my time with my kids.