You know you wouldn't have to make use of functionality just because it's there, right?
In this case, it is the ability for an app to install and execute arbitrary code that hasn't been reviewed. I download an update to DoodleJump and it installs some malware on my device. I'd be none the wiser.
I don't want that stress, which is why I chose an Apple device. It protects me from that scenario.
Go look at your settings?
As the recent leaks showed, the walled garden didn't protect you from invisible malware