The best answer you’ll find is Pascal Precth’s one who explained that on a dedicated issue asked in December 2015: “Do Observables make sense for http?” (but feel free to read along, plenty of additional answers are really good too!)
On top of my head:
– Retry
– Cancel
– Enjoy all the Rxjs operators
– Possibility to combine them as streams
– Thinking reactively in your whole app
– Consistency
– Observables are cold by nature, no need to wrap them like Promises into a factory function if you want to trigger it later