There is a big "it depends". The more clients that attach to the client side of the mesh, the more the performance degrades. The more mesh traffic that is passed, the more time cycles it takes away from mesh performance. That is just speaking in general. how much it degrades depends on your setup and environment.
I would not serve client traffic on a mesh radio just to sidestep that possibility (my opinion). If you cannot control the number of clients that will attach to a mesh radio and how far away those clients are, you might just want to avoid it. There are enough variables that you need to keep in mind on a mesh link. You should just serve clients on the non-mesh link.