You don't need to use Action="Clear"
unless, as its name indicates, you need to clear the value of a property.
Basically, when you omit a value from your notification, it keeps the old value. For instance, if you decide to remove the count from the tile and send:
<wp:Count></wp:Count>
Then it won't actually remove the count but keep the old value. It's convenient because it means you only have to send with your notification the values you want to update. And when what you want is really to clear the property, and not keep the previous value, you just have to add the Action="Clear"
part:
<wp:Count Action="Clear"></wp:Count>