What is the "Custom?" checkbox used for in DocType?

Community Documentation
1

Hi all,

I have been poking around with custom checkbox in the DocType settings.
The only behaviour I was able to identify was that if document is “custom” it does NOT create any directories inside module for particular DocType. Following this developer has no controllers “available” (can create files manualy though).

Any other things connected with custom checkbox?

Cheers