Every single thing involved in making and playing games has an influence on how the game plays - absolutely everything - from the system its played on to engine and the code and scripts it uses.
Thus they all extremely important to the end gameplay quality.
i.e. Absolutely every single character of code in the engine, source, game code, scripts, sound, texture, sprite or model and everything else added will potentially reduce playability.
Thats why if you keep adding you will grind to a halt - no question about it. Try it, just keep adding stuff.