Pros - can stimulate people's appetites, can relax people, lots of different ways of getting it into the system
Cons - what's the real effective dose (Cheech and Chong size joints or just a small one, or better yet, a pill of xmg strength THC); for those that smoke it, are the health risks associated with smoking non-filtered smoke worse than what's wrong with the person; do they just want it because they're junkies and "nothing else works for me" that you get with drug seekers; fat soluble drug, so stuff can keep coming back (could also be a pro - maybe a little sustained release) - hard to regulate in the system properly; can build tolerance so therefore need more to get the same effect. There the legal embuggerances of having to carry your LTT - License to Toke and Transport (not in that order) and where you get the stuff.
Don't get me wrong, I feel there is a place for this stuff, especially with some diseases, like advanced/terminal cancers. When you give someone anything, you have to be pretty sure what the intended effect you want is, what the odds of harm coming to someone are and what both people involved hope to gain, all while taking the best available evidence to support you decision...people don't realize that alot of physicians aren't going to prescribe something if there isn't good hard proof of what something does and what the minimum safe and effective dose of a given medicine is. A wise man named Paracelsus once said all medicines are poisons; only the dose determines poison or remedy. The jury is still out on good dose vs bad dose I believe.
There are lots of other things out there besides drugs to hep with pain - the best pain docs deal with the mental as well as physical side of things...and there's the rub - people don't want to do the work that comes with staying healthy. They just want to take a pill or light up and hope everything goes away. People don't want the advice their doc has for them, which for the most part is really what alot of people need - they just want that magic Rx pad.
Sorry to all for sounding a bit preachy (and long winded) - I'd say the same about alot of medicne we give out as well that are actually legal.