When mediators are trained and accredited, we are encouraged to have a joint session, if not at the beginning of, then at least early on in, the mediation. However experience shows that such sessions need to be carefully considered, and if they are to take place, carefully planned.
Some mediations are successfully concluded without the parties meeting at all. Some benefit from a long joint session, possibly taking all morning. Some benefit from a joint session early on, some later in the day.
The key for the mediator is to ask the question, discuss with the parties their views and before any session takes place check what is going to be said. The key for the lawyer and client is to do the same.
In two instances where I dispensed with a joint session, the parties were initially surprised, as the lawyers had assumed there would be one, and so advised the clients. Mediation is a flexible process, so we use our discretion, linked to experience and commonsense, but always in cooperation with the parties.