Voting for
@Pootie22's response.
I have rented to numerous roommates in my house. My observations/experience:
1. In practice, I normally give a "pass" (no charge) the first time a roomie is late, IF they communicate ahead of time. This does support that I value communication, which I do, because it reduces surprises and allows me a smooth path to resolving problems in general. I say, "thanks for communicating, that's important to me. I won't charge the late fee this month if you pay according to your new plan."
2. If there is repetition, or lack of communication, or they slip from the new payment schedule, I invoke the late payment charges.
3. Twice I've had people who were periodically late. One had a self-management issue. The late payment fees were necessary and not always sufficient to keep lateness from extending longer and longer. At one point, when I delayed invoking them, the late rent piled up and when I tried to discuss/collect, renter complained to a local tenant advocacy center. The good news was that when they read my agreement and my documentation of the circumstance, they told the renter I'd been more forgiving than necessary; there was nothing to complain about. Due to experience, I knew the guy would catch up if I let him/ pushed him now that he was working again... and if he left, I'd lose collection leverage. I figured I was better letting him pay rent plus $100 catch up per month. It worked - he eventually paid in full. We agreed on partial late fees during the catch up period, so I profited a couple hundred dollars due to successful resolution. By then, relations were fraying due to other issues. At that point I terminated the lease. It should be noted that I essentially have month to month leases with all roommate/renters, so that I don't have to put up with crap if I don't feel like it.
4. The "catch up" case above illustrates the principle other posters mentioned - an occasional late payment is meaningless if you have cash and the renter makes good on it. I have a current roommate who works on tips and occasionally is short. Every few months he asks for a few days late. The lost interest is tiny, the loyalty keeps turnover low (aka, means that he puts up with my low tolerance for his TV noise). Peace and prosperity abound.