PMI stands for Product Manufacturing Information and originally coined by SDRC back in the '90s.
As for the advantages, there are many and we can always discuss in more detail if you e-mail me direct. The basics are (when truly Y14.41 compliant)
1. No BASIC dimensions - saves time & reduces clutter & no mismatch with the 3D model
2. Easier for a single FCF to be associated to numerous features - saves time
3. Faster to dimension directly on the model then to "switch over" to drafting typically with a whole new set of menus to learn and use.
4. Superior communication - 3D models are easier to "read" and clearer then 2d line drawings.
5. Fewer files to manage
6. Downstream applications (with appropriate translators or compatability with other applications) like CMM programming/reporting, tolerance analysis
There are more!
But if nothing else - common sense advancement
GD&T Instructor / Consultant
Applied Geometrics, Inc.