AVG_OF_ANY is the flexible counterpart of
It gives you the average of the values you provide in between a set of brackets, each separated by a comma.
If a value is not available:
AVG_OF_ANY simply ignores it and gives you the average of values that are available
AVG, before returning a result, will alert you to go back and provide the missing value.
This expression will give you the average number from the three types of personal income mentioned.
If the person in this case does not have any income from wealth gain, the outcome will be the average of the other two sources of income.