Standard MTB Sizing.

[Dirtbreath]

"The horizontal distance from the bottom bracket center to the top of the headtube centerline

is referred to as reach. The vertical distance between these two points

is known as stack. By comparing the reach and stack on different frame

models, the rider is able to identify exactly how their bike will fit

and feel on the trail. This system eliminates any uncertainty created

by the seat tube angle, and forever drops the need for ?actual? and

?effective? top tube measurements. The reach and stack of a frame is

the most important sizing information for a freeride or downhill rider

but it is extremely valuable for trail riders and XC racers as well."

 

 

http://www.pinkbike.com/news/08ReachStackStandard.html

 

What does this mean? Is this relevant/necessary/good move?