You should only do this on websites that actually require it otherwise you're almost certainly going to cause more problems than you'll solve.

Messing with the UA header is going to get you flagged by every bot detection tool because when you change your header from "Firefox on Linux" to "Chrome on Windows" your fingerprints don't add up anymore and you look exactly like a poorly written bot. You're likely going to see more captchas, you might get blocked or rate limited more often, and get placed under increased scrutiny, orders held for verification, silently filtered or shadow banned, etc.