This is a Quality-Of-Life mod, Automatically sets AutoStrut modes and other part options as you build your vessel.
This mod has a GUI for better control how it behaves, or can be left to "Automatic" operation if you want to set & forget
"Automatic" mode will:
Set the root part to the Heaviest part, left alone as a bug prevention; "Heaviest Part" may cause problems.
All parts connected to the root part will have AutoStrut set to the root part,
All other parts will be set to Grand