Breakdown of Он успел хорошо распариться.
Questions & Answers about Он успел хорошо распариться.
Успел + infinitive means managed to do something or had time to do something before some limit.
So Он успел хорошо распариться does not just say that he got steamed up thoroughly. It adds the idea that this happened in time, before something else interrupted or before some situation changed.
A simple past verb would describe the event itself. Успел adds the nuance of success before a deadline or cutoff.