I read in Dr. Andrew Cook's book that he often needs 3 hands for surgery, so he has an assistant gyn. I highly recommend the book, it spoke to some of what you are asking re: excision surgery. http://www.stopendo.com/

I know that my OBGYN referred me to an endo/fertility specialist because he knew that this other doctor could help me more then he could. Some OBGYNs will work along side a specialist so that they can refer their patients and stay on the case with the specialist along the way. Everything we have done/talked about since last year, my OBGYN knows about because the specialist keeps him informed.

Not all obgyn are knowledgeable about endometriosis or fertility issue so sometime they will refer you to an obgyn who expert in that area and get better provide you the care you need. I have experience that my 15 plus years with endo

Proably incase one see something the other one may miss.Do has extra training.Like a second opinion on the spot.Proably in case of problems too.One better than one.

As far as the two doctors some doctors just work with another doctor. I had surgery and there was another physician in the surgery with her.