It tells you who is currently online in the dashboard (ability to make it viewable to public), with members/guests/bots online and gives the IP address, current URL viewing and the referring URL.
This is great to see where people and bots are currently at on your site.
I use it, but I don't display its content to the public. If your website is having good traffic, it is okay. But if it is low on traffic, it can be a discouraging factor to visitors. They'll simply conclude that not much is happening when they discover they are the only one visiting all through their stay on your site.
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