Differences between win 7 deployment in vms and physical computers

For win 7 deployment, says we use MDT (lite touch) with WDS.

What are differences between win 7 deployment in vms and physical computers?

What problems can physical computers face that vms do not have?

For physical computers, there will be network latency. For vms, writing to harddisks will be slower than in physical computers.

If I need to deploy win 7 in real life to physical computers and suppose I finish testing deployment in vms, do I need to test deployment in lab using physical computers?

Thanks.