In my case Xfinity kept the same IP for me for two years, then an outage happened where everyone in the neighborhood lost connectivity. When connectivity was restored I got a different IP.
I feel like the biggest difference is the fact that there's no guarantee that the dynamic IP won't change, so all systems need to be prepared for that, or you need to be mentally prepared for that day.
At what point does a dynamic-but-unchanging IP become functionally static?