Why is the SID the same on all newly imaged machines?

I've been reading and reading but I don't understand SID changer.

I noted the SID on the machine just before taking an image.
All machines having that image restored onto them have the exact same SID as the original.
I've tryed clearing it from the ISD.

Windows 7 64bit /ZCM 11.2.4

Perhaps I just misunderstand the purpose of SID changer.

Can someone explain it ?
Thx