The Wikipedia article about Faraday cages has this anecdote:


  A Faraday cage was used in 2013 by the Vatican to shield the Sistine
  Chapel from electronic eavesdropping during the secret papal conclave
  to elect the next pope.
  
  Source: "Papal Election: Vatican Installs Anti-leak Security Devices at the Sistine
  Chapel".
  International Business Times. 2013-03-10.


My question is, what would this accomplish? I can see two motivators: they either don't want what they discuss to become public, or they don't want people to have any inclination as to what the decision is leaning towards before it is made.

If it's the first motivator, a Faraday cage won't help. Hardware could be recording and transmit when the cage is removed or be retrieved at a later date. If it's the second motivator, it's probably a better question for the Catholic stackexchange, but I do not know of any reason why this would really matter (are people making huge bets on the outcome? If so, why does the church care?). 

Is there some other reason for the use of a Faraday cage I haven't thought of?

When you read up on the source quoted in the article, you will notice that it apparently isn't talking about a "real" Farraday cage around the Sistine Chapel (putting a whole building under a wiremesh dome would be ridiculous even for the Catholic church) but rather about a figurative one in form of:


  the installation of equipment which blocks any electronic signals from getting out of the Sistine Chapel.


The author doesn't seem to be very tech-literate (see second to last paragraph), but it appears like he is talking about GSM jammers or similar devices which make cellphone communication impossible though active interference, not passive blocking. Such device are available commercially over the shelf for affordable prices. By the way: such devices violate broadcasting regulations in many countries making them illegal. But the Vatican is a sovereign state, so they don't have that problem.

The main motivation for this measure was that during the last conclave in 2005, the election of Pope Benedict XVI was leaked to the media before the official announcement. This is what the Catholic church wanted to prevent from happening again in 2013 and this is why they took technological measures to prevent anyone inside the conclave from communicating with the outside world until the official announcement.

Leaking information later was a secondary concern.
