Heap determines cost of service based on monthly visits instead of the more common data point based pricing that incentivises tracking less data points to save money.
Cohort analysis allows you to compare things like user retention over time, what kind of progress has been made with that retention over time, how many people perform certain actions from a set starting point over time, etc.
After adding a JavaScript snippet to the site, Heap captures every event that you can organize later instead of having to define events upfront. It means that if you decide to track something new you have data from the past as well.