Depress portioning valve while bleeding?

[6SENSE]

I never heard this before, or did it before, but I recently read in two books that you are suposed to depress the spring-loaded plunger on the front of the proportioning valve while bleeding. Is this true? Is it necessary?

 

[Red Regal T]

I have vacuum brakes and I didn't depress the plunger to bleed the system.

 

[salvageV6]

Yes you are supposed to push the plunger for bleeding.

I believe all it does is cut down on the time necessary to bleed.

I have bled them successfully both ways.