The best way we can explain Attribute Templates is with an example. Let's imagine that your world has lots of Locations, and on many of those locations, you want to remember to create a custom Attribute for "Population", "Climate", "Crime Level".
Now, you could easily do that on every Location, but it can get tedious, and you might forget sometimes to create the attribute "Crime Level". This is where Attribute Templates come into play.
You can create an Attribute Template with those attributes (Population, Climate, Crime Level, etc), and later apply that template to your locations. This will create the attributes from the template on the locations, so all you have to do is change the values and not have to remember about the attributes!