Once again proving my newb-hood or newb-ness... If your the champ and you have a belt or belts. Don't they make you defend your belts? If so how often does this happen. Like Pavlik is fighting Lockett because he has to. So how does it work?
You're better off going to the different organisations websites, they list the conditions there. My pick would be the WBA, fascinting reading. Especially the Regular champ/Super champ part. If you decipher it, let us all know what it means and how it works. Also, you won't find anything on corruption or bankhanders in those manuals but that is probably the biggest influence on mandatory defences etc.
It depends on the organization. The WBC requires that you defend their belt twice a year and at least once a year with the mandatory challenger. All of the rules have clauses that essentially mean that they can make up whatever rule that they want on the spot so you'll see that this isn't always the case.
Whenever those **** sanctioning bodies feel like it, or so it seems. This is one of the things that disillusions some fans, all the alphabets, and their differing rules. Some will force mandatories and strip in double quick time (IBF), others are more relaxed and protect their champions (WBO)
Whenever you stop being profitable to them. **** Vitali turned down a mandatory and retired and the belt is still there waiting for him whenever he wants it. Mayweather has not fought at 147 in quite some time and shows no intnetion of going back any time soon and his belts are still safe simply because he is a profitable guy to have carrying your belt.
the SuperChamp belt is given to a unified champion because the WBA recognizes that when a fighter holds many belts it is difficult for him to fulfill his mandatory defences. The WBA then has its next top contenders fight for the Regular belt, and the regular champion is then the one who must fulfill mandatories for the WBA at that weight class. When the Super Champion is no longer unified, if for example he has been stripped of his other titles, then he must fight the Regular Champion to determine who is the one and only WBA champ, as was the case with JMM when he had to fight Chris John. I actually think its a good rule.
Each organisation has an asterisk next to pretty much any important rule saying that the rule can be overturned in special (aka profitable) circumstances by the board of directors.