If it's not storage we're trying to save, it's battery. This is definitely one hot commodity in the iPhone world and it seems like we're always trying to find more of it. It's now completely normal to carry a charger and a power bank with you where ever you go, just in case your battery dips into the dreaded below 20% range. We're always into new tricks that can help us save as much as possible, so try out this one next time you're in need.
Go to Settings > Battery to view a complete list of every app that is sucking your battery life dry. They'll be presented in order of how much power they're using, so you can kill the main offenders if you're not currently using them. You can also switch your phone over to 'low power mode' within battery settings, which is another helpful boost.