Sure, if you are calling from your cell phone but are going to be out of range (in a basement or a tunnel) you might leave a message for someone to call you at the office when you get there. (Or if you know your phone is going dead for lack of charge.)People don't always want to be called back at the number they are calling from.
Probably a good option for drug dealers/buyers who don't want to leave anything other than a number on record. Could be similarly ideal for mobsters, adulterers, covert agents (the real ones, not the Valerie Plames).
Under what basis do you say that Valerie Plame was not a real covert agent? Do you work at the agency or having any idea what you're talking about? Even if her husband is a slimy, ambitious jerk, you do not, repeat, do not reveal the identity of CIA operatives. We are at war, and especially during times of war. It doesn't even matter if she were a covert agent -- the same would be true if she worked in the cafeteria.
In the old days, we would have taken the people who revealed her identity and lined them up against a wall and shot them.
If my wife was really a covert agent and I wanted to help maintain her status, I would a) try not to get caught in so many public lies and b) try not to introduce her at numerous dinner parties as "my wife, the spy."
And if I was myself a (female) covert agent and wanted to maintain my status as such I would a) not secretly hire my husband for a less-than-secret intelligence mission and b) not let him then write an op-ed about it in the NYT.