Platforms allow you to separate and organize the values of your global variables, and to filter your monitorings results.
Let's say that you have two platforms Production and TheBeta, and imagine that you have a global variable PHONE_NUMBERS used in many tests to select which number to call. You can decide to call a different number depending on whether you're running your test on Production or TheBeta platform.
Apart from variables, platforms are also useful to filter your monitoring results. You can choose to see all results, or only results of monitorings running on platform Production or TheBeta.