Basically, to prevent rotation snafu’s. Category rotations are always a formula based on two things. 1) the number of songs in a category and 2) the number of times the category is used in the clocks and format week. M1 is highly accurate with its rotations. What you see on the Average Turnover grid is what the rotation will be for every song in the category. Now, say you have a Recent Gold category that is working just great with 75 songs in it. All the songs are flowing through all the dayparts just fine. But it could well be that a small change in the number of songs could totally change the pattern for the worse. 71 songs in the group might result in them all falling into the same daypart over and over. Or, maybe 78 songs would result in each one failing to play in a certain dayparts.*
If you told the software to automatically move three songs out of the category on the first of next month, but didn’t tell it to move three songs in to replace it, how would you know the rotation was going bad? One M1 user said, How about having it tell me if something like that is going to happen?” The problem there gets down to the individual. Something that is unacceptable to one guy might be perfectly okay for another. Only you would know with a new rotation pattern is a ‘problem’. We can’t figure a way to get M1 to read your mind. So, this is the kind of thing you really need to be doing yourself to keep on top of your rotations.
If you are manually moving songs into and out of categories, the Average Turnover grid is one click away. It is a screen you should be checking pretty regularly.
(*yes, m1 does have rules that will prevent songs from repeating in the same daypart but it is inefficient to have a category that is structured for daypart repeats and then to have a rule that says ‘don’t let that happen.)