If you are just going to play a supported system, you don't need a custom character sheet. On the other hand, you can use the custom character sheet to add tabs to existing character sheets if you want to run a game with mechanics that aren't supported by the base sheet. Well, access to the api is basically the ability to run specialty javascript segments that enhance the functionality of Roll20. From generating initiative rolls for all selected tokens at once to synchronizing movements between 2 maps to being able to alter token settings or character sheet values with a macro to... well, a lot of stuff. If you know how, you can write your own, but there are a lot of them available. If you look through the api forum, it should give you some idea of some of the things people are doing. Quite a few are available through a drop down ready for use once you are a pro subscriber. <a href="https://github.com/Roll20/roll20-api-scripts" rel="nofollow">https://github.com/Roll20/roll20-api-scripts</a> You didn't ask about it, but one of the most useful tools that is available as a pro subscriber is the transmogrifier (assuming you ever run more than one game). Yeah, you can upgrade at any time. You can downgrade, and pro will continue to the limit of what you paid for and then drop down to whatever you continue with from there (plus/free).