When you start getting into larger size tanks, you may find you need to add multiple heaters to get what you need. e.g. You might need 3 x 250W for 220G.
You then configure them so that they are staggered, e.g. one at 74F, one at 76F, one at 77-78F. That way they don't all run simultaneously, saving $$$ on electricity.
A large water volume will take time to cool, so you can afford to have one (or two) of the heaters doing the grunt work, and if it gets really cold then the other one (or two) kick in to 'assist' the primary so to speak.