roger williams benefited from founding rhode island because he could express his views there, something he could not do in england, and at least 2 other settlements in the new world.
as far as england benefiting, the only thing i could think of is that they could rid themselves of people who did not want to be under the thumb of the ruling 'religious' caste.
since farming was difficult in RI, shipbuilding, whaling and fishing were the main ways of making money.
they would build and sell ships to england, and probably sold/traded whale blubber, and possibly salt preserved fish to/with england.