McAfee SiteAdvisor, later renamed the McAfee WebAdvisor, helps you to keep safe your PC from threats while using any browser, it also helps to protect you from phishing and malware attack and does not affect your browsing performance.
Basically McAfee SiteAdvisor scans websites and determine whether it is dangerous or not, it is a browser plugin that gives website safety rating and secure search box, allows users to surf, search and do other activities.
Sometimes you accidentally click on malicious links, while browsing, it blocks malware and phishing sites.
if user type the wrong website address, it alerts and direct you in appropriate route.
it scans your download and alerts you if there is any risk.