PERFORMANCE

Stana Katic isn't a cop, but she plays one on television.  And as a pretend cop, it's Stana Katic's job to put away the criminals, the filth and the scum of the earth with a smile on her face and a dance in her step.  Criminals are only good for one thing and one thing only---To be arrested and warehoused away inside a prison.  There are only three modes allowed to a criminal---About to be arrested, being arrested and has been arrested.  And as a pretend cop, she looks for scum who deserves to be arrested for acting like a temper tantrum throwing creep (Not all criminals throw temper tantrums, but it helps to discredit the jerk if a temper tantrum is thrown) and proceed to ruin that jerk's life until the jerk gets the punishment that the jerk deserves. 
However, being a pretend cop is easier than being an actual cop.  A pretend cop gets twenty-two booklets that are forty-five pages long each to memorize.  Recite back the lines of dialogue into a camera and it's recorded for eternity.  It's as easy as that.  Actual cops need to interview witnesses, gather evidence, search crime scenes and search other areas that might contain evidence.  Pretend cops always gets the criminal.  Actual cops doesn't have nearly as much an easy job.  Pretend cops gets to say dialogue to criminals that an actual cop would be tossed off the job for.  Pretend cops in a cop show don't have to wait until the courtroom trial to find out if the criminal they arrested actually gets to stay in prison.  Plus actors such as Stana Katic as Detective Kate Beckett gets paid much more money than an actual cop, she lives in a better house (Both on and off the screen) and she gets to wear much better clothes too.