Roll cage x brace?

Can someone tell me exactly what is the purpose of the x-brace on the roll cage?Beside the xtra support of the upper shock mount support.Has anyone ever attach the bracing from the main hoop to a stock inner frame rail or is mandatory to mount it to the upper shock mount .I'm considering up dating the cage on my e-body with a x-brace.do u all think that the x will keep the stress cracks on the rear window/side rear glass to a minimum?Sorry 4 the many ?'Inquiry minds like to no.Thax In Advance.

The X bracing is to keep the car from "racking", its
very important, usually in a chassis car there is more
than one... to cover different planes... like down in
the bottom behind the trans and the one that goes down
to the shock brace... that one keep the main hoop
from racking side to side..... remember the magic word
in chassis work "triangulation"