In general there are two ways for companies to make money. 1) They make something that otherwise wouldn't have been made, or make it more efficiently than the competition and then capture volume with lower prices. 2) Rent seeking; they extract higher profits from the same activity, e.g. by buying their competitors and raising prices.

Traders do the work of finding the companies that can do one of these things and allocating resources to them so they can do them. When it's the first one, the societal gains are quite significant. When it's the second one, well, there are supposed to be laws against that and if it's happening then we need better laws or better enforcement.