This option refers to the camera order in your final tour. The default value is 1, which means that all cameras have the same priority. Therefore, they will be played in the same order as they appear in the Objects window. You can manually order your chosen tour cameras by assigning them individual numbers, or you can create priority groups that will then play in the order in which they appear in the Objects window. (E.g. all priority 1s play first, then all priority 2s, etc.)