This question already has an answer here:
Today I learned about Sea Launch, essentially a launch pad floating on the sea. (Pretty crazy, right?)
What's cool about that is that you can launch from the equator without the tricky part about your country being on the equator.
So, say, hypothetically, SpaceX* made their own floating launch pad on the equator. Obviously it would be costly to make, costly to transport the rocket there, and there's possible pain in the neck with ITAR requirements, etc…
But what's the upside? How much extra performance could you squeeze this way vs launching from Cape Canaveral (or even more southern Boca Chica)? Say you want to launch to a geostationary orbit, how much more payload could you carry?
* - Or anyone else for that matter