Some Questions About SQL Backup

In SQL 2005 SMO
documentation, there is a DeviceType enum:
http://msdn2.microsoft.com/en-us/library/microsoft.sqlserver.management.smo.devicetype.aspx

It
seems there is no doucmentation about 'LogicalDevice', what's the
difference between that and 'VirtualDevice' ? (for the latter, I guess
we need to implement a VDI driver)

Another question is that,
suppose we want to backup a database to a hard drive file, I could use
either T-SQL or SMO, what's the advantage of using SMO?

Thanks!