to allow something to happen on a large scale; to trigger a chain reaction
"When the security flaw was leaked, it opened the floodgates for hackers worldwide."
to have a burst of energy after feeling tired
situations or decisions that involve a lot of risks but also...
to write something quickly for later use
to reduce spending; to save money due to financial constrain...
to start something, especially a project or task
to make the best of the situation you are in