Android has an option allowing the users to install apps from any source. (You could install whole third-party app-stores this way.) Do you know of anyone who

Android has an option allowing the users to install apps from any source. (You could install whole third-party app-stores this way.) Do you know of anyone who uses it? However, it's always there, so, if my favourite Android app gets deleted from the store, I could still install it. If your favourite iOS app gets deleted by Apple, what choices do you have?