There are many outdated views/misinformation in this thread.
- AV programs' power-consumption is negligible
- Android is popular and mainstream...which means more targets, more undesirables, more malicious logic in the wild (see chart)
- Security software isn't always just AV; most have other handy features as well
- PUP detection/Adware: I'd rather find it
before my phone number, etc. are leaked
- Permissions prompts are useless as we're desensitized to them and they aren't specific or granular enough
- Google, Amazon have stated that they are not policing their markets for malicious logic (though stuff has been removed--after-the-fact); I assume this will change (as the above link shows) but we're each responsible for our own security
- There are garbage security apps and there are AAA ones, with 98%+ detection rates
- AV apps update signatures just like PC ones do
cf.
Mobile Security Reviews
cf.
AV-TEST - The Independent IT-Security Institute: Android
Personally, I use avast! as it is a top-tier malware detector and it has nice extra features that I use (Firewall/Shields, SMS/Call block, anti-theft, Privacy Adviser, PUP detection when they add it) and I use TrustGo Ad Detector for unwanted spyware detection.
Chances I or my wife will run into malicious logic are really low; however, there's no downside and all upside to having a solid, free security app.