usage of business configuration sets (bc sets) and transport requests

Hi,

can anyone explain the sense of business configuration sets regarding to normal transport to me? I looked at a lot of help pages (also at the help.sap.com link) but I found no satisfactory answer to the question when I have to use BC sets and when I use the normal transport requests (se09/se10). Or when I have to use both.

Thanks for your help,

Fabian