The main reason for sysprep on a large network is SID/CMIDs for the machines. If you plan on using a KMS server then you will have issues in activating the machines; similar to this [url]http://support.microsoft.com/kb/929829[/url] . Even if you have rearm counts remaining these SID/CMIDs DO NOT reset on a /rearm. If you use WSUS then these will all share the same CMID so again the WSUS database will incorrectly report the status of each machine. If your client machines need something from the enterprise CA these will report an incorrect CMID pair when issuing certificates.
Personally I would get the image sysprep’d with /generalize
I discovered this the hard way after W7 was released. I moved from XP to W7 thinking I could use the same tricks in W7 that I did in XP (and W2000)- use GPOs to reset the IDs with utilities - but you cannot.