You can read about it on the wiki. It is something like if your MMR is 3+ steps above where you are, you skip just about everything. They want you at your real MMR as fast as possible so they will jump you whenever possible. At the end of last season I went from a Bronze 1 placement to mid Gold in like, 30 games with a 76% win rate. Was making more than 30 LP per game. Was losing like, 5 LP. Was like, 10 games (With like, 8 wins) to get out of Bronze 1, then with my newly inflated MMR I was getting tons of LP for Silver 5 wins, 5 games with 4 wins to promo series, win series with two wins in a row, skip to Silver 3. 3 wins to promos, lose one win two, skip to Silver 1.
I did have to play my Silver to Gold promos though, and I even lost them the first time because I was playing with high Gold/low Plat players. But it placed me at a LP value where a single win put me back in promos. Was shooting me through Gold too before I stopped playing ranked.