In the part of Santiago de Cuba where I was staying, it was very common for houses to have their doors, windows and balconies protected by metal cages (known as rejas). The installation of these was carried out by private individuals and it seemed to be good business, as they were much in demand.
Many were very decorative, which led me to conclude that they were primarily installed due to their aesthetic value, rather than any risk of crime that needed to be guarded against. However, one night at the house above which my apartment was situated and whose front entrance we shared, the owner of the house was awoken in the early hours and observed a masked man attempting to gain entry and cutting the wires to the buzzer that sounded when the gate was open. The intruder ran off when he saw that he had been observed. After that, I was glad that my apartment was protected by its own cage, attractive or not.
Tales of the Heroic City 
People spend hundreds of CUC on these, and, indeed, all in an effort to stop thieves. I can’t think of a single Cuban friend who can’t recount a tale of being robbed, mugged, or at least pilfered from. Stolen items can be as basic a pair of shoes left unattended for a minute, a shirt from a clothes line, a pen from a desk. Cubans rarely leave any item of value loose, in the open, or unattended.
I did not get the impression that muggings are a common occurrence although, having said that, a Cuban friend was robbed at knife-point of the trainers that he was wearing whilst I was there. Clearly, though, many people feel it necessary to live behind cages, which must show that they believe that theft needs to be guarded against. Nothing unique to Cuba, of course. Here in England my neighbours and myself have burglar alarms and car alarms and would not dream of leaving doors unlocked or things of value on display.