As a new user, I want to know what is the purpose and significance of setting the random number seed to a fixed value so that each result is the same

When I use it to calculate the eigenvalue, I try to add some code to output some information about each particles. However, I found that each recalculation has same results and same particles’ information. For this, I what to know why use the fixed random seed. And the purpose and significance of the results have repeatability. Thank you!