I really don't know other than to say you need to be able to get around the table. I'm always amazed at living rooms where there's about 8" between the couch and the coffee table where you'd have to almost slide.

Read somewhere that the ideal was 18 inches. I like it a bit closer because I like to lie on the couch and read, and sometimes I come close to missing the coffee table when I am reading and blindly reach out to put the cup on the table. If you get it too close then knees get gouged on the corners by people walking between the couch and the table.
Basically, sit on the sofa and see if you can comfortably place something, like a plate or wineglass on the table. Then get up and walk around it and see if that is comfortable.
You may be bigger or smaller than whoever made the above rule, and you may have more or less room for the table. 18 inches is a good starting place but it isn't written in blood.