No, that's correct.
If you aren't using the history system, the Config.history.maxStates property should be 1 in every circumstance I can think of.
This still doesn't necessarily mean it's a great idea to go nuts with variables, but it should prevent any noticeable slowdown on most browsers, as far as I know.
At that point, making your game more efficient is a good idea, but not necessarily going to have a heavy impact on performance. A smaller variable store also helps limit the size of saved data, meaning more reliable caching, especially on mobile, and faster download/upload of imported and exported saves for users with slower connections.
It's also a good practice to be in if future projects you make require the history system.