Windows 7 - sysprep

Hello experts,
I've just been introduced to one of my clients who has an onsite local engineer supporting the 50 of users/machines at this particular site
The site has been having all sorts of issues relating to roaming profiles for thier Windows 7 users, as well as machines not registering in wsus console
Found out the the way this tech is deploying machines, his essentially cloning machine without any Sys prep, and his admament this won't cause any issues, can you advise if this would be correct, what are the disadvantages of not Sys prepping a machine before capture, what sort of issues can it introduce further down the line