There's quite a lot of general background information here, but the upshot of it all seems to be that the neuroprotective effects are useful in diseases like MS:
Public release date: 14-Oct-2007
Contact: Professor Raphael Mechoulam
European College of Neuropsychopharmacology
The endocannabinoids: Functional roles and therapeutic opportunities
Cannabis (marijuana) is the most widely produced plant-based illicit drug worldwide and ...