If you take selfish human-only view, nothing good there. But there is tons of them and they are important part of food chain even if they are tiny.

If we could selectively just eliminate those 2-3 sub-species that transfer malaria, dengue and say zika or yellow fever from human perspective the negative impact on environment compared to positive impact on often weakest and poorest part of mankind if... well incomparable. Ecosystem would take a hit but I can't seriously put half a million of human lives yearly, often small children, against some blip in our environment, which would in few years balance itself out into new equilibrium (probably with more insect of some other type taking the place) and choose insects.

What I would eliminate outright without any remorse are ticks. They are not that important in food chain, and are scourge for both humans and many animals.