Firebase Notification - send to user segment vs send to topic difference

I am assigned a task to use Firebase to implement push notifications but I am kind of new this.

Looking at the documentation:

https://firebase.google.com/docs/notifications/android/console-audience

I can't tell under what circumstances should I use send to user segment or send to a topic.

Can someone please give me some example when to use one or the other and point out the difference? Thanks ahead :)

Solution

Use User segements

To typically send push notifications to a specific and limited set of devices.
Message delivery is almost instantaneous (in my experience). Also, I haven't observed throttling as was the case earlier with GCM.

Use Topics

Topic or publish/subscribe mechanism is used for a comparatively larger audience and the information type is public. Examples are weather and news.
Topics have latency (Message delivery may be throttled)