It is recommended that you  factory reset your MacBook
pro  or  MacBook air   if
you are selling it, if it is performing unexpectedly, or if there is a bug that
is taking up too much space in the internal disk. The process of resetting a  MacBook Air  or  MacBook Pro  can
be overwhelming for new users or for those who have never factory reset their
MacBook Air or MacBook Pro. In the process of  resetting the MacBook pro  or  MacBook
air  to factory defaults, some
essential data may be lost. There’s no need to worry! Throughout this article,
we have provided you with a detailed guide on recovering your  Mac data .

This is an important
security measure that you should not skip. Even if you trust the next owner of
your laptop, your Mac’s hard drive is packed with sensitive information you
wouldn’t want to be accessed. It’s always possible for malware to sneak into
your system and gain access to your personal information.

Read the full steps here: https://www.soldrit.com/blog/factory-reset-your-macbook-in-4-easy-steps/