When you tram the head, do you typically shoot for perfection, or do you leave a small amount of pitch to compensate for spring, deflection, etc? How much and which direction(s)?

I recall reading that Bridgeport targeted a small amount of forward (I think) tilt during manufacturing and that is the reason for the question.

What are the theories/practices?

Looking for advanced info here, not the basics.

Thanks!

Scott