This script can be used for making a leather streaks.
How it work:
1.Make an edge selection for streak base.
2. Press "Profile" button to create outline edges. With red line in curve control change the shape as you wish. It's will updates interactively in viewport
3. Press "Depth" button to push center in\out. Blue curve control the extrude amount. Increase "Depth multiplier" spinner value to push it more or less.
4. If you don't like final result press "Undo". The previously saved model will be revealed.
p.s.if "delete edges" checked - first and last edges will be deleted to create quads.
The sofa streaks from picture below was created with this method. (Taken from http://alex-3dvisual.blogspot.ru)
In the attachment archive there are a test piece of sofa mesh provided by Alexandr Tolmachev.