Autonumber() adds 1 for each new distinct value of the field respectively field-combination. By combining it with rowno() it could respect further dimensions, for example not just returning a number for a product or customer else returning such a number per day or category.
But it's seldom useful because the performance of this approach is already by smaller data-sets quite worse. Therefore if such information is needed it's better to use interrecord-functions like previous() or peek() within a sorted resident load to create such results.
By using rowno() within the autonumber() the rowno() becomes the counter against the specified field-combination. In general autonumber() need no sorting but in some cases it could be useful, for example within a calendar by applying it against Year & Month to get a continuous counter over years.
Creating a dimension-specific counter is rather seldom useful - just regarding to your example it seems not be needed. Even by your applied AutoNumber(Name&'_'&Place&'_'&Value) I have some doubts that you need it.