You'd think that a tally would keep a score (tally) of a specific item, but actually it's a Key-Value store. However the values can only be numbers.
We're using this to see:
what products the customer has looked at the most. This is a standard Tally where each Key is the product ID, and each value gets increased by 1 for every product view.
what products the customer has looked most recently. This is a tally where each key is the product ID and the value get set to 0 (zero) first and afterwards the value get's set to the current timestamp in ms. This ensures that the last looked at product always has the highest value (the timestamp)