This depends on the situation and the participants. Some employer’s attorneys enter a mediation for a discrimination case only for the purpose of finding out what evidence the employee has against them. People who enter mediation for this purpose are not prepared to work toward a compromise, and their only purpose is to gather information.
On the other side, there are some employees who refuse to compromise. They are at the mediation only because their attorneys told them to go. These people ask for an outrageous amount of money or for things that are impossible. Worse, there are some employees who lie. They lie in the information they provide their attorneys, they sign complaints that contain lies, and they continue to lie throughout the mediation process.
Mediations that are successful are ones where both parties come into the mediation willing to try to work out a compromise that gives both sides something. There is no way to determine if mediation will work before you are in the middle of it. On a positive note, though, when mediations do work, employees can get more money in a settlement than if the settlement occurs after the employer has paid money for litigation.