Building from bottom up as opposed to ADMT?

I asked in another thread about using ADMT to conduct a move from Windows 2003 domain to Windows 2008 R2

What about the option of just NOT migrating anything and manually recreating all new users in a brand new domain? 

Let's suppose I create a brand new domain, manually recreating all the usernames from the old domain (knowing they are all different) and going from there?  Are there any advantages/disadvantages to doing that?  I also have a file server and an Exchange 2003 server in the old domain as well.