It's just an easy way to look at the tests so you can look at all of them in one location and be able to see patterns of slowdowns and such.
BTW, when you look at the results (when you are signed in) you may see some that are highlighted in yellow. Those results aren't yours. They are people's who happen to be on the same connection ID at the time that they ran their tests. If you are seeing the other ones and you want to be able to see just yours, scroll all of the way to the bottom of the table and just under it, on the left, will be an option to click on to show only YOUR tests. Why testmy defaults to showing you other peoples' speed tests along with yours on the results page when you are signed in is beyond me. It seems like the default should be to only show yours. I guess nothing can be simple these days. LOL.
Also, only YOU see the other tests (the ones in yellow). If anyone else looks at your results page they will only see YOUR test results, not the others.