In my experiance with cheato the more I have the more growth I get to harvest. I used to harvest down to a softball size chunk and it would almost seem to stop growing after a harvest for a while.
Now I harvest every waterchange so every 3 weeks, I only havest down to about a half full 29 gallon tank so around the size of a basketball, by the end of 3 weeks the tank is almost full, so I pull out about half of what I have every 3 weeks or so. I never got that kind of growth with a smaller ball. It just seems to grow better for me from a bigger chunk.
I have never had cheato die, so I guess I don't worry much about it dying and releasing nitrates back into the water.
How big is yours? how big could you let it get?