If you are in a game where you don't commit on time AND don't provide a single order to you units you will be marked as absent and the game will stop waiting for you.
If you join a game with an initial "everyone's ready"-phase and don't mark yourself ready, the game will boot you and go back to being open for someone else to join.
In both cases you will be booted from all forming games that you happen to be in.
The server now assumes that you aren't actively playing, and it will try to increase the quality of the forming games by removing inactive players from them.
Best,
Martin