It is important to redo experiments for numerous reasons. You check your results from the first time the experiment happened, and if they are not the same you know there's something wrong. You ensure predictability and correctness.
To make sure the results can be replicated. If you do an experiment and get a specific result but do the experiment again and get a different result that usually means there was a flaw in your original experiment. This is why one must redo it.
