Raspberry Pi 4 doesn't need a fan. People just like to put them on because because micromanaging CPU temperature is part of the hobby for some. Yes it might throttle its CPU speed when going full tilt for some time, but lets be real how many workloads require poor Raspberry Pi to be loaded 100% for prolonged periods of time?
If it throttles CPU it means by definition means that a fan helps. Also constant heat increases failure rate.
Cycles of heating and cooling are what increases failure rates. The thermal expansion and contraction causes issues.
That's one way to put it.
Another way is that my great grandchildren won't care about inheriting my collection of hobbyist SBCs, and therefore nor should I.
Permanent heat doesn't?
From what I've gathered, heat absolutely does[1] affect[2] it[3]:
Subsequently, in 1967, Black of Motorola experimentally derived a median time to failure (MTTF, i.e., operational lifetime) model for EM in Al interconnects, showing that the time to failure due to EM is inversely proportional to both the current density and the absolute temperature of the interconnect.
[1]: https://infinitalab.com/blog/ic-failure-analysis-defect-type...
[2]: https://resources.system-analysis.cadence.com/blog/msa2020-b...
[3]: https://www.mdpi.com/2079-9292/14/15/3151#sec3-electronics-1...
Thermal cycles, heat, current, all contribute to degradations and failures. It just so happens that cycling is the worst and everyone knows "it's the power cycles that kills computers". Doesn't mean at all that electronics can't be damaged countless other ways.
Running plex/jellyfin :)