Antivirus apps for Android: Worthwhile or does caution suffice?

Google’s Android operating system is like a house with open doors. Unlike Apple's iOS platform, Android allows anyone to develop and distribute an app – even without going through the official Google Play Store. 

What is a boon for independent programmers can be dangerous for users, since apps containing spyware or malware can be inadvertently installed on the phone. Antivirus apps are available, but are they any good?