Originally Posted by CPH-Flyer

You can get your boarding pass in the app, and that will negate the need to visit the check-in counter if you don't have luggage to check-in. At security they will want to verify your boarding pass and passport, and same again at the gate. But other than that, there are no formalities.

There might be some destinations where they don't want to issue the boarding pass until your travel documents have been verified, in which case you'll get an "online check-in not available" kind of message.