This is going to seem like an incredibly simple question, as I know users can already exist in multiple groups (and I know it's best practice for them not to do so where possible). I am very new to SharePoint and am still getting my hands dirty with all there is to know. Here goes:
The person running the project I'm on asked why we couldn't use the existing AD group for the lowest level permissions that are planned for a sub-site since it would have all the members who require access. In this case, each business unit has an AD group so his plan would be to use this AD group to get everyone access, and then select single users out to be defined as Members or Owners (or whatever SG's are defined). Can SharePoint support this without generating a ton of the permission warnings about a user having conflicting permissions, or are they inevitable given this design?
I know this could fall into the cardinal rule of not asking an opinion question, however I think this would draw upon learned experience more than anything else.