If your an expert, a cover photo is important to add because it helps beautify your page and engages users to follow and learn more about you.
For users, a cover photo can often provide the same function as it can for an expert, but can also be a fun addition to your page that is unexpected!
In general, add a cover photo that is relevant to your lifestyle, your passions for beauty, fitness, skincare, etc. or your overall personality. For instance, your cover photo could be of your favorite yoga pose, your makeup collection, your favorite hairstyle or makeup look, and more!
Here is an Example: