Using a nose clip whilst swimming is really down to personal preference. Some elite swimmers choose to wear them because it allows them to stop water going up their noses and can help them to have a more effective underwater phase.
The same approach applies to any stroke and nose clips can be a helpful tool if you’re struggling to breathe while training and racing as it can be a good way to provide a more efficient oxygen intake. Many argue that they don’t do anything for your street cred and that might be right, but who care if you pop out a new swim PB?
What are the advantages of nose clips?
The main one is that it prevents water travelling up the nose during all strokes, allowing you to focus on solely breathing through your mouth; they can also help alleviate any allergic reactions to chlorine.
What are the disadvantages of nose clips?
Your breathing, and therefore overall physical, efficiency decreases; water can get trapped up the nose and contribute to more snot production; bad breathing habits can get ingrained.