Catia V5 surface

Hi,
Could somebody explain me what is the difference between a Catia V5 file which contains surfaces using the GSD workbench only and another file which uses Body-in-White or/and class "A" surfacing? When is necessary to use Automotive class "A" and BIW workbenches for creating surfaces instead, of GSD? Or when should I create a Catia V5 file, using both the GSD workbench and Automotive class “A” and/or BIW workbenches?
Thanks!

[chinacatia]

I have catia materials including the followings:

catia v5 r17 sp3 Software 2CD
catia v5 r17 Help document 4CD
CATIA v5r17 Training 20CD
catia v5 A-class surfaces, Reverse engineering,advanced video courses with demonstrations of car 15CD .
Otherwise there are some other training courses, about 20CD.

These CDs are not for free. If anyone wants to buy, please email to service@chinacatia.com.

http://www.cdpan.com.cn/vip/auto_body.rar
http://www.cdpan.com.cn/vip/test.rar
http://www.cdpan.com.cn/vip/catia.rar

The above URL are just part of demostrations.

CATIAÖÐÎÄÍø chinacatia.com - ÌÔ±¦Íø This is my e-shop.

[buckmaster]

BIW is the exterior surface of a vehicle when its developed by our OEM's. They like to use the color white because it shows highlights the best . Class "A" surfacing is not alway's used just for sheet metal. Class "A" is almost always used for any visable, touchable surface that has to be reviewed by studio before being able to complete your part.

Hope this helps...