HARRY BUCKLEY writes:

My 2 zone aircondioning has 2 units outside. I noticed one fan seems
to be going faster than the other. The amount of air coming out of the
slower one seems less.

Possibly a botched repair, wrong replacement part.

What effect does this have on the system?

Wrong condenser fan: overheating fan motor, ineffective heat transfer,
reduced efficiency. Many $100s of cost over the long run.

Assuming these are originally identical units!