Brake Master Cylinder rubber retainer,do I need it ?

What is up with the little rubber piece you get when buying a Brake Master Cylinder. I remember it being a retainer for keeping the pushrod from falling out of the master,but only for manual or Power Brakes...I cant remember which.

The car the Master Cylinder is going on has power brakes,Do I need this little rubber retainer or not?

It's just to keep the pushrod in for manual brakes.

For power brakes, it's not an issue.

Thanks Oz,I couldnt remember.