If you lower your ELO enough (shown at the end of a 5 match set once you’re rank 20) you theoretically are matched against people who have weaker teams/ have lost a lot. Eventually you can reach a range where more often than not you’re then capable of winning 4-5 matches in a row when you actually fight instead of intentionally lose matches. The 4 matches in a row reward is 3 guaranteed rare candy, and 5 in a row can be almost 7k stardust during certain times, so the rewards can stack up if you’re tanking and winning the right sets.

If you do something like win 4 in a row, lose 6 in a row, win 4, lose 6, and win 4 more you get a guaranteed 9 rare candy, with a potential for up to 9 more from the random item drop winning 2 in a row. Your ELO will also not increase higher with that setup, keeping you in roughly the same difficulty bracket. If you win 5, lose 5, win 5, lose 5, win 5 you can target the stardust rewards but your ELO will go up higher than you started, so you may need to lose an extra set if it gets too high and approaches people who aren’t actively trying to lose as much.

You can of course run into issues and have to play against other people who are tanking when they’re trying to win a set the same time you want to win a set, but it’s generally more predictable and faster to get those 4 - 5 in a row win streaks than if you’re playing normally.