What reasons are there for being concerned about companies like google and meta etc collecting data and tracking me?

Please understandnim asking this question from a genuine place. I dont want the quora answer, i want the tech savvy, security expert minds of my fellow lemmings. If thats ok?

What happens to this data? What can/do they do with it? and why are so many people concerned about google tracking them?

Do i as an average user need to be concerned?

If so, What sorts of things can i do to avoid being tracked? Preferably without too much comprimise.