[aembleton]

I used to do this when I had a rooted phone. I kept the radio active so that I could receive calls and texts but data, GPS and wifi were all off.

It saved battery if I wasn't doing much with my phone. If I was constantly unlocking to check where I was on a map then it ate up more battery and it was incredibly frustrating as it takes a while to get a GPS lock when you don't have Wifi to assist in a city, until Wifi come back on which also takes a while. Friends that only communicate with messenger and Whatsapp had trouble getting through. Loads of apps that had been trying to communicate also woke up once there was a connection using up more CPU cycles, slowing everything down some more.

IMHO, its not worth it. Just use the background apps controller in Android 8.1. Whitelist the things that you do want notifications from and everything else can wait for you to open the app.