When I'm implementing ConfigMgr 2007 at customers, default collections are almost not used. Only the "All Systems" is handy for recognizing devices. Mostly I create collections for existing or new Active Directory OU's. (for example: Desktops, Laptops, VDI). When devices are placed in this OU's you can browse for this. Use "Active Directory System Group Discovery" for that, and the query can be created.
Read the blog: "Configure dynamic collections in ConfigMgr" for a complete guide to create dynamic collections.
But what to do when there are no devices found in OU's, or worst, the OU's doesn't yet exist? In that case you cannot browse for this, so queries must be manually filled in. If you are specifying a full path, the FQDN of the Active Directory domain and a path to the OU is used to locate the OU in question.
So, in my example, the path is "SYSTEMCENTER.COM/VIRTUAL MACHINES" for the OU. With this information it's not needed to link ConfigMgr collections to existing Active Directory OU's anymore!