Mine run 24/7 on low for a few years so far, one is going on 3 years and the other is about 8 months. No issues other than periodic cleaning and filter replacement. Main hint: keep a spare filter before California fire season.
I check my indoor air quality and I only have to raise them to medium/high when air quality is bad outside (winter temperature inversions, summer fire season) or when cooking (often don't bother but I'm not as sensitive)
I have asthma, allergies, and pets so.... yeah. Medium it is for me.