It goes without saying that is a good idea to keep your primary email address private. Spammers, snoops and hackers alike want to know your email address so that they can exploit it for their own gain whether by targeting your inbox with advertising or with phishing, spear phishing and spoofing attempts.
There may be times when you want to use temporary email (aka disposable email or fake email) which can be especially useful when you are reluctant to share your primary personal email address.
Apart from keeping your email address private and undisclosed, you also may want to keep the contents of your emails secure and away from snoops and other prying eyes. Email remains as popular as ever but, if sent unencrypted, emails are an insecure means of communication.