Authenticity in politics is a winner. If you can fake that you've got it made.
The show gives politicians an unparalleled opportunity to offer an apparently intimate glimpse into their "authentic" characters, while leaving them in absolute control.
No wonder it is rumoured - and flatly denied - that spin doctors closet themselves for hours with their leaders helping them make their selections for the show. ("No Ed, He Ain't Heavy He's My Brother is not a good idea").
Still, considering the subjects have complete freedom to choose whatever music they like with them to the fabled desert island, it is extraordinary how many of them still manage to give revealing insights into their characters which they later live to regret.
David Cameron and Benny Hill's Ernie, who drove the fastest milk float in the West, springs to mind along with the entirely un-spun (really?) Tangled Up In Blue by Bob Dylan. And, yes, he really did chose the Smiths' This Charming Man. Morrissey was not amused and later banned Cameron from liking his band.
Margaret Thatcher once claimed Rolf Harris's Two Little Boys was her top tune, until it came to Desert Island Discs, when it gave way to Beethoven's Fifth.
And it is not just the music that can prove awkward. Nobody who heard it will ever forget the moment in 1996 when presenter Sue Lawley asked Gordon Brown if he was gay.
So, when Ed Miliband's turn came this weekend, Westminster was agog. Well, a bit agog.
He insisted the tunes were all his own choice, and looking at the list there is little doubt. That, of course, doesn't mean they are his genuine favourites - we've all got that well-played copy of I Lost My Heart to A Starship Trooper hidden away haven't we?
What he did reveal was, unsurprisingly, a pretty safe selection including the left-wing anthem The Ballad of Joe Hill by Paul Robeson, the South African national anthem Nkosi Sikelel' iAfrika and - wait for it - Jerusalem.
There was some schmaltz with Robbie Williams' Angels, dedicated to his wife Justine, and the genuinely appalling A-ha just to prove he really didn't have a girlfriend at university.
The closest thing to a confession was his admission that relations between him and his brother, David, were still not right after he beat him to the Labour leadership.
"It was hard. Hard for my family, hard for David, very hard. But I suppose I felt that it was the right thing," he said.
Asked whether things were healed he said: "Healing, healing."
Mind you, he did chose Edith Piaf's Je ne regrette rien as one of his discs.