The airplane thing is interesting because planes are expensive (and airlines are for-profit), so they are careful about utilization and keep planes as close to

The airplane thing is interesting because planes are expensive (and airlines are for-profit), so they are careful about utilization and keep planes as close to full as practical. Which means if you board that plane, you are altering some stats that someone, somewhere is watching pretty closely. You could easily be helping to tip the balance toward adding another flight to that route or switching to a bigger plane for that flight. I don't know the right math, but I would assume this averages out to something near 1-to-1. That is, if, in the steady state, 1000 people take extra seats on airplanes, presumably it averages out to about 1000 seats of extra capacity being added. And I suppose the concept must apply to low-ridership bus lines. If you ride it, you could tip the balance toward keeping it going rather than canceling it or consolidating it together with other routes. Maybe this is a bit less than 1-to-1, though, because transit agencies aren't just following rider behavior but also trying to fulfill a mission to have good coverage of an area. TLDR, maybe it does matter if you're near a utilization threshold that someone is really paying attention to.