Pascal's wager, for one thing.

How's this? (I'm thinking here that the smallest unit would correspond to 1 possible arrangement of the Hubble volume, so the unit would be something like 1/10^70 or something. Any other state of the world is meaningless since it can't exist.)

As usually formulated, Bayesian probability maps beliefs onto the reals between 0 and 1, and so there's no smallest or largest probability. If you act as if there is and violate Cox's theorem, you ought to be Dutch bookable through some set of bets that either split up extremely finely events (eg. a dice with trillions of sides) or aggregated many events. If there is a smallest physical probability, then these Dutch books would be expressible but not implementable (imagine the universe has 10^70 atoms - we can still discuss 'what if the universe had 10^71 atoms?').

This leads to the observed fact that an agent implementing probability with units is Dutch bookable in theory, but you will never observe you or another agent Dutch booking said agent. It's probably also more computationally efficient.

Good answer to help me focus.

If probability has a smallest divisible unit, it seems like there would have to be one or more least probable series of events.

If I was to anticipate that there was one or more least probable series of events, it seems like I would have to also anticipate that additional events will stop occurring in the future. If events are still taking place, a particular even more complicated series of events can continue growing more improbable than whatever I had previously thought of as a least probable event.

So it seems an alternative way of looking at this question is "Do I expect events to still be taking place in the future?" In which case I anticipate the answer is "Yes" (I have no evidence to suggest they will stop) and I think I have dissolved the more confusing question I was starting with.

Given that that makes sense to me, I think my next step is if it makes sense to other people. If I've come up with an explanation which makes sense only to me, that doesn't seem likely to be helpful overall.