There are three settings to the experiment status:
In Progress means that you are still working on the experiment and that you still need access to make edits.
Complete means that you don't intend to make any more changes to the experiment. The timestamp that the experiment was locked will be noted. If you realize you do need to make changes, changing the experiment status back to "In Progress" will allow you to make changes again, but the timestamp that the experiment was locked will be replaced by whatever time you lock the experiment again.
(in 2 months, when you mark an experiment as Complete, you will be prompted to notify a colleague to "witness" that the experiment was complete by signing off on that experiment.)
Blocked means that you are no longer working on the project at the moment, due to constraints. You will still be able to make changes to the experiment, but blocked experiments will be pushed to the bottom of the Project stack.