IMathAS-libretexts

The most important reason for the use of random allocation of subjects to the different treatments is:

to ensure that each subject in the trial receives the best possible treatment.
to guarantee that approximately the same number of subjects is assigned to each treatment group.
to protect the experimenters from legal action in the event that the experiment goes drastically awry.
to ensure that the different treatment groups are as similar as possible in every way except for the treatment received.
to guarantee that the results of the experiment can never be duplicated.