Unique visitors statistics

It’s not out of the box as far as I know, though we have similar reports available and I’m sure you can do a lot with a Data Explorer query.

What would you be using it for?

Be wary of comparing it to e.g. Google Analytics on your website, since they will be using different assumptions in their calculations. (e.g. we’d be consolidating IP-addresses/devices based on user name, while GA would be blissfully unaware of usernames).