I never understood the giant focus on side windows. If you want to see your components while you're using your PC, why not just build inside a transparent case, or build on a workbench/open style (caseless)

ATX spec is designed for positive pressure/airflow, so you’ll generally run hotter in open air.

Why would the hardware care if the pressure is higher in the case than ambient? How could it even tell?

Positive pressure means less dust.

Specifically less dust if you have filters on the intakes. Positive pressure means you'll have air coming in where the fans are blowing it in (through a filter), and any gaps in the case where there aren't filters will have air flowing out due to the pressure.

If you have negative pressure you'll be sucking in air through the gaps and that air won't go through a filter, hence more dust.

Is this really part of the ATX spec though? Or just something people have learned to do for modern cases with air filters?

Do you run linux at the moment? I've personally found my switch to CachyOS from Windows 11 one of the biggest factors in making my PC run silent/near silent. Happy to elaborate if you're curious.