Ember addon Vs normal package

I am trying to understand the differences between an Ember addon Vs normal package more from consuming side in my app.

So I would like to understand the following points;

1. Differences in consuming both ? like what do we need to import, Brocfile changes, etc
2. Is the installation process same for both ? Can both of them live in any repo or registry (like npm or bower registry)
3. How do we decide whether to package something as addon Vs normal package (this is more from a developer perspective)?

You can also highlight any other significant differences.