Developer Mode is a security feature. It will prevent unsigned code from running on your device — apps that are not on the App Store, app marketplaces nor TestFlight. Most people can enjoy the added layer of security for free. But, this also means that if you’re writing your own apps in Xcode, you will need to enable Developer Mode on your iPhone or iPad before running your app.
There are also a few apps you can only install by side loading onto your device from a Mac, using an app like Sideloadly. These could include apps that aren’t allowed on the App Store, such as Hot Tub, a porn app; or apps that are no longer available from their original developers, like Apollo, the former Reddit client. For side loading to work, you’ll need Developer Mode enabled as well.
Read on to see how to turn it on.