Playing all of your letters first is one of the key strategies to winning a close game. The end game rules are similar to those in the popular board game. There are more details on this topic on the Help in game. Be sure to check out the Strategy tab. I put the summary below. Thanks!
The game ends when one player plays all their letters and there are no letters left to draw or when players pass for 3 consecutive turns. The player who plays all of their letters receives all the points left in their opponent’s letters and those same points are subtracted from the opponents score. This effectively gives the player making the last play double the points left in their opponent’s hand.
It would not work well if you played all your tiles and had no tiles to draw and then the other player got to play until they were out of tiles. This adds a strategy of trying to make the last play even if its not your biggest points and also to not to get caught with big points in your hand.