Often after the fallout of the divorce there remains an inner turmoil of doubt and ambivalence that is helped by simply talking it through, one to one, with an experienced professional.
On the other hand, sometines it's helpful to talk through practical problems with your Ex. Understanding, empathy and reaching an agreement and compromise are very hard when you have both struggled through a bitter divorce.
However, if you have children, there may be no escape. There will be times when talking together in a safe, neutral, place with an experienced professional is especially important, both for you and your children.