

You only need to reduce it if it will interfere with another one of your WAPs. In most cases, auto power settings are fine.
Typically you’d reduce it if you had a high density environment with lots of devices (IE office building) because one WAP and network cable can only handle so much traffic, so the WAPs can load balance or have reduced coverage to split the load.
Hopefully they’re far enough apart then, otherwise you can actually reduce performance.