The more filled board is - the higher are multiplier for the points. So the "oval" combo is a good escape plan to keep somewhere in corner unfinished just in case (that's how I like to play it) and fill board a bit for extra points, something like in the original tetris when most players keeps one empty column and waits for the best moment when to place that "I" piece into it.
As there is no real goal, just pure competition in leaderboard - I decided to not heavily strict player from any combos, let player just embark the flow of the game, clear mind, meditate. I think all of them (combos) are kinda OP in a manner of clearing the board. I recorded a video of me playing and showing all the combos, mechanics and how I prefer to use them when I play.