The basic run down:
So the pros which have been mentioned:
It can be heavily controlled, with a punishment = to removal or ban;
You can turn it off, so you don't have to see someone's PAC look and you can still rely on descriptions;
It enhances immersion;
Allows for quicker replies (not having to read descriptions);
Could possibly be tinkered so you have a prop limit;
I'm 90% sure if a prop is black-listed it cannot be used on you;
Cons:
RP > Script, (if RP was 100% greater than script we could all use DarkRP to great efficiency, yes?)