protection of yourself and loved ones (as even if someone inevitably finds out, at least you have a focused point to guard as opposed to having to defends yourself from all angles) both from harm as well as bias and prejudice
the opportunity to be more than just yourself and create a symbol for people to inspire them as well as a legacy
the ability to work outside the law when needed which is usually the super-hero MO
Cons:
misunderstandings which on the small scale lead to hurt feelings and on the large scale lead to fights with people who would otherwise be your allies
creating a legacy
getting on the wrong side of the law due to misunderstandings
it allows for a good deal of trickery and mistrust between heroes depending on how tightly kept the secret is