Consulting a lawyer helps you know where you stand if you have to go to court and what you might expect to happen at what cost.
Lawyers also write letters arguing why they think the law might be on your side and will try to get you the best legal outcome that they can. However, most people have busy lives and concerns about fairness and practicality, as well as legal rights.
Mediation isn’t like a court hearing, there is no need for legal argument. You know your situation best, and so in mediation you will be invited to respectfully discuss what is important to you, listen to the other person’s views and suggest anything that might help to resolve the conflict in a way that takes into account the needs of both of you.
You remain free to take legal advice whenever you wish.