Do I need flux if my solder has flux?

Do I really need to use flux if my solder already contains flux? I've noticed that some types of solder are labeled as "flux-cored," which suggests that they already incorporate flux into their composition. Is it sufficient to simply rely on the flux in the solder, or are there additional benefits to applying flux separately? I'm trying to streamline my soldering process and minimize the number of materials I need to use, but I don't want to compromise the quality of my joints. Can you clarify this point for me?