I think you'll get dramatically different answers to this question depending on who you ask. You'll need to examine how you are using attributes and what expectations you have around attribute propagation to determine how appropriate globals are.
When our IdM implementation was first rolled out by a consulting group, they used globals very sparingly. We have since retooled most of the workflows to use globals and seen dramatical simplication of form management and addition of new resources. It is important that you distinguish variables in a resource that you might not want affected by globals with unique names.