I like having the diverter because without it, the main drain doesn't do anything.
With it, I can sometimes get away with brushing the stray leaf at the drain and watch iot get sucked away. I don't need to break out the vacuum and hose. Also, it improves circulation in the deep end, which minimizes that temperature stratification you sometimes get wherein you dip your toe in the pool and it feels so nice, and then you jump in and discover it's four or five degrees colder down a few feet.