What's the difference between sourcePaths and importPaths in DUB?

[WhatMeWorry via Digitalmars-d-learn]

The documentation doesn't go into much detail:

sourcePaths	"<path1>" ["<path2>" [...]]	Allows to customize the 
path where to look for source files (any folder "source" or "src" 
is automatically used as a source path if no sourcePaths setting 
is specified) - note that you usually also need to define 
"importPaths" as "sourcePaths" don't influence those