Birds like game birds, some water birds like ducks, loons, etc are able to go to safe places with lots of easy food and lose all of their feathers at once, eat like crazy and regrow them all at the same time. They are flightless at that time but can usually survive, so the strategy works for them. Most other birds molt sequentially, i.e. all their flight feathers in a sequential order until the molt is done. Very large birds with huge flight feathers use the strategy discussed above. I find molt interesting. Are you a birder? If so check out @birdersofsteem.