The fact it's free to use and the intelligence of the Chrome extension to recognise the type of application or website you're using, meaning less time is spent altering. It also recognises when you're using non-web based apps too such as Word/Excel which is very useful.

Tracks your daily productivity and allows you to see how you actually spend your time

The clarity and depth of the data is really useful; it's easy to get all the information I need to form my own useful conclusions without it being too predigested and indecipherable.