Minimal. It frankly just doesn't actually advance his goals very significantly. Nor is he a particularly clever man that thinks of unusual strategies.

I think his focus is on squeezing his current userbase more than any kind of long term caring about the size of it. Wouldn't be surprised if he plans to quit his job in the next 5 years and collect a fat severance anyway. He'd rather people not leave, but DDoSing a small chunk of people somewhere else doesn't really help much.

This is a random attack, so ask yourself who benefits? For one thing, it's fun. It also pisses some people off. It also irritates a fairly politically active population.

Who wants all those things? Trolls, of course. Why are they, specifically, trolling? Varies individual to individual, but mainly it's about causing pain to others.