One extremely big reason to avoid playing solo whenever possible.
If you get put on a team with a 4 premade they will probably not only blame you but report you after the match if the game is a loss.
I really try to que with at least 1 other person (as a 2 premade) because of that.
Of course the 4 reports from that match alone will do nothing to your account, but those can stack up fast if you play multiple hours a day and meet 4 premades a few times daily.