It is something of as tradeoff. While your battery life will improve, apps won’t update in the background when you have the Background App Refresh setting off. This means that the updates that your apps usually make in the background, whether they are sports scores, stock market prices, or the latest temperature, won’t update until you open the appropriate app and the app updates. In other words, if you open your sports app, you might not be looking at the most up-to-date score right away.
If you feel that you don’t need your apps to update in the background, or don’t care if your full-screen effects auto-play in the Messages app, you might want to see if you can greatly improve your iPhone’s battery life by toggling off these features.