Paul Stamatiou makes some good points on Android’s benefits and some less good ones:
Each app has its own interactions, design and purpose as it should. Android helps coalesce each of these siloed experiences together into something a bit more fluid. The back button allows you to navigate through your history of pages, apps and menus. Didn’t mean to do that? No worries, no cognitive load required, no need to parse how that new app implements its navigation or drawer. Just hit back.
Remember the first time you discovered those shortcuts in Ikea? Felt pretty neat to save time navigating through a useless section when you knew exactly where you wanted to go. That’s Android and the back button.
Any iOS app worth using has a clear hierarchy with back buttons when it needs them. If a user is totally lost there’s the home button to completely start over. Every user knows how to work it.
A back button that occasionally takes you back pages in apps, occasionally takes you back in your history, and then occasionally takes you to the home screen is just confusing to users.
Metaphors are hard.