Cake balls do not have to be refrigerated and can safely be left out at room temperature.
However if your cake balls have perishable frosting on them then those cake balls with the perishable frosting need refrigeration.
But if the frosting on your cake balls are not perishable then you do not need to refrigerate the cake balls.
Cake balls with perishable frosting should be eaten the same day for the best taste because when you refrigerate cake balls the taste can change and also the refrigeration of the cake balls can cause condensation on the coating and this moisture will cause the coating to become sticky.
If you make cake balls and want to use perishable frosting it's best to just add the frosting on the day you plan to serve or eat the cake balls.
Cake balls will usually last for up to a month or two months at room temperature and only a few days in the refrigerator.
It's best to eat the cake balls soon after making them because the longer you keep the cake balls the more stale they become.