I don't know about iOS but a modern Android will periodically delete permissions from apps you aren't using, the app stays installed but it's now just a harmless icon and wasted storage space as I understand it.
I keep 'lean' devices, the apps that I actually use, battery lasts from days to weeks (phone, tablet respectively) and NoRoot Firewall (on Android) makes sure that my phone stays 'silent' to the apps and target IP-addresses of my choosing.