When you put virtual machine to particular OU, you may refer to virtual machine properties, such as 'server role', 'server group' or 'user group'...etc. It's easy to set a drop-list in blueprint of vRealize Automation Center (vRA) to let users choose this kind of properties but hard to create a computer account in corresponded OU location in vRO. That's because vRA passes most of values to vRO as strings, Active Directory workflows in vRO do not provide a way to convert string to OU.