Theme customizer allow you customize the site real time. You can see the changes at same time you make any change in customizer settings.
Most of the options in customizer are coming from the WordPress core, which allow you to customize site information, logo, menu, widgets, static front page etc.
We added header settings in the customizer. It will allow you to adjust the logo top & bottom space adjust and main menu items top , bottom, left and right space adjust.