When it is adding something to boiling water, like pasta, when you add the pata there is a temporary decrease in temperature, because the pasta is room temperature, so if the water was only at a simmer, it would barely have a bubble when you add the pasta.
For some foods it probably makes a difference chemically on how it cooks, but even if it doesn’t it certainly would reduce cookig time. Simmer helps food not scald on the bottom of the pan, and is easier to monitor, also helps dense or thicker foods cook through properly. So, it might be less practical to boil foods, which would seem to take the least amount of time, but a boil at the start, when there is a lot of liquid in what you are cooking may not harm the food in any way, and speed up cooking time.
If we go back to the pasta example, boiling constantly doesn’t work because the starch will boil over. Recomended cooking times are started at a boil, then simmer. But, there is an old lasagna trick to just sit the noodles in hot tap water for 20 minutes before layering into the lasagna pan.