Isotype control antibodies in Flow Cytometry
I don't believe that the Isotype Control Antibody makes the antibody bind more specifically but rather ensures that your signal is specific to your antibody.

The Isotype Control Antibodies tend to bind to the non-binding domain of the antibody, typically the constant (Fc) domain. By measuring the concentration of the control antibody, you can determine what percentage of your light signal comes from your primary antibody and not from non-specific binders to your light source.

This is very similar to having secondary antibodies in your assay.

Random link showing that I'm not making stuff up