Yes yes, I know "but allergies!" "but dust!!!"
Personally, I have not noticed any difference with pollen allergies because I like to keep some windows open- once you open up the home to airflow, purifiers cannot keep up with incoming air. If I relied on AC for cooling, kept all doors and windows closed and ran lots of purifiers quite fast, and regularly used a filtered vacuum cleaner like an OCD mofo, I'd probably reduce interior pollen counts. But I walk outside too, so my immune system will get hit with a sledgehammer every time I step out the door even if my home was hermetically sealed. So allergies- maybe, YMMV.
Dust- purifiers are not designed for house dust, they don't have high enough airflow.
I still have 4 purifiers and 2 particle counters brought over from a move so I'm well acquainted with measuring and controlling interior air quality. I've turned one purifier on a handful of times last year for nearby backburns, just because it's already sitting out in the living room.
Edit: Hm, I too bad threads cannot get voted on. I was hoping to see how many people would downvote this.
Edit edit: Ooh, a poll!
bro is obsessed with AIR
https://www.ozbargain.com.au/node/770978