You're definitely going to save much of the time of developing a custom design, using this tool.You can customize colors, layout types, header design, backgrounds, fonts etc. with the click of a button. No CSS/HTML editing
To start customizing navigate to "Appearance" > "Themes"
On Themes page click on Customize button.
Clicking in customize button will take you to frontend with customizer button shown
Click on cutomizer button will show a panel with required tools to customize the theme.
You also get an option to reset the styles as they were before the customizer was launched.
Here is a quick demo of how theme customizer works.
https://crowdvox.com/wp-content/uploads/2016/11/frontend_designer.mp4