The only time I've used the Alexa app on my phone is to disconnect a bluetooth headset from an Echo so I can use it with my phone.
Edit: Voicecast can be useful for weather. Asking the Echo about the weather, I end up with a seven day forecast at a glance on the tablet!
There was a tutorial for Alexa that popped up after registering the device and in the process was a link to Voicecast information.