Want to skip the idle, incremental gameplay?
Want to build anything and everything right now?
Want a separate save file for a different creation?
Want to make better Twitch stream marble races?
Want to support independent game development?
Buy the Sandbox Mode DLC!
The Sandbox Mode is a separate save that you can activate whenever you like. It will initially copy over the marble tower you are currently using but afterwards, you can use it to build whatever towers you want and as many as you want! Heck, you could probably break the game with the freedom Sandbox Mode gives you.
Be aware that Sandbox Mode more or less turns the game into a toy! You may never want to go back to Normal Mode. There are no exclusive unlocks in Normal Mode, everything is available in Sandbox Mode and there are likely to be new features exclusive to Sandbox Mode in the future, such as multiple save slots and pre-made tracks to use for the Twitch integration marble racing.