While 10.3.10 was a full installer, the hotfix refinements (often referred to in community circles as "R3" or similar revision markers) targeted specific operational bugs that plagued professional HD environments:
The R3 hotfix is specifically designed for Mac users running Pro Tools HD 10.3.10. If you are experiencing issues with your current setup or want to ensure optimal performance, it is recommended that you install this hotfix. Avid Pro Tools HD 10.3.10 R3 hotfix only For Mac
The 10.3.10 update (including subsequent hotfix revisions) resolved several high-priority issues: Plug-in Sync While 10