Modularity requires additional overhead. That’s just the way it is. If you want to semantically separate different components of your web app or theme, you have to include files, run safety checks (e.g., include_once), extend components that you only use 20% of, etc.
WordPress encourages this behaviour, if you have plugins that only effect your admin panel, the files still get included and the actions and filters still get included, the functions are still defined, for every frontend visitor page render — but they are only called into action when you’re on the backend of your site.
And lately when coding for WordPress, I’ve come to embrace and accept that it wants me to be modular and extend. Continue reading Performance overhead of using plugins and includes in WordPress