Action Sequence tells the current state that before you tell the next action in the stack to 'go'... wait for the current action to be finished completely.
Think of it like foot racers in a line, but some Overseer walks across the starting line and says "ok, you go" then that racer runs all the way around the track and back to the start and says "ok, I'm back", then the Overseer steps to the next racer and says "alright, your turn, go"... Until all of the racers have gone. The actions take turns and only one can run at any given time.
This means that any action that has "every frame" turned on will stop the sequence since it never finishes.
It can also happen just as fast as normal, so it could appear that there is no difference technically, but there is indeed.