Someone who wants to steal from your premises may first want to check out how good your security is. One way they may do that is to visit your premises to observe and check what you are doing to protect yourself. Is everyone entering your premises (both outside spaces and inside) there for legitimate reasons and how do you know?
If you have CCTV installed it acts as a deterrent because they will not want to be observed and identified. If you don’t then the first you may know about it is when the actual theft occurs.
By installing a good CCTV system, and monitoring what it records, you not only improve your security you can continue to improve it proactively.