What are the real goals of using cell phone jammers?

Cell phone jammer is typically used in places where, for security reasons or forced silence, mobile signals are blocked, preventing them from ringing.

VVIP movements have cell phone jammers in their vehicles and at the site where the VVIP is present. It's to thwart remotely triggered bombs, etc.

Banks use it in their main cash corridors to prevent thieves from communicating with outside accomplices.

Convention centers use it when they are fed up with asking everyone to turn off their cell phones (easier to block signal)

In some specialized examples, hospitals use it - in CCU / ICU

Some countries have rules federated by their telecommunications authorities as to where and when a cell phone jammer can be used. Irresponsible use of cell phone jammers can wreak havoc with a cell phone carrier's coverage maps.