Basically it means that they can handle lots of cases at the same time while still giving each one as much attention as it needs. Winning or losing a difficult case can often be decided by how much time and expertise you can put into it. When you have a lot to lose, would you rather have a team of lawyers, each specializing in a different aspect that’s relevant to the case or a single lawyer who is overworked because he‘ll have to prepare a different case after lunch?
Edit: typo