I’ve come to the conclusion that it really doesn’t matter, if I win or lose in my placement matches. I could win or lose all 10, and I’ll still have the exact same amount of SR as last season, so why are they really there?
I might just be way off though, so what are your experiences with PM?
10 comp games at your level or very close. No real importance. Why folks think arbitrary calendar dates means they deserve radically different SRs is beyond me.
Thank you very much 
My alt ended 3942 and i just got placed with someone who career peaked 3300 in placement matches. This game is a joke.
They do matter!
I had an old bronzeish account and decided to place it for fun, it gained 225sr in placements c:
…however 90% of the time you’ll just be 50-100 sr +/- from where you ended last season.