I'm a big fan of ridgelines. They do 3 things for me.
1. Help me set the proper sag.
2. Support my bugnet (required in Florida year round).
3. A place to hang my glasses, headlamp & water bottle and sometimes, bear spray.
As to length, my hammock is 11' long which I consider perfect for my 6'-1" height and my ridgeline is 9'-5" (111") long. I use a MacCat Ultra Spinn tarp with a 12' ridgeline.
Some day I'll spring for a cuben tarp but it will have at least a 11.5' -12' ridgeline. But what I find fascinating about hammocks is that there are no two alike once we all start tinkering with them.