The term "best practice" refers to a way of doing things that is recognized as optimal ("best possible") by experts who have studied such matters. In traditional website usability studies, ordinary people are watched as they perform tasks on the web. The usability experts watch and learn; when the greatest number of people can succeed in doing a task, they analyze what made the web page so easy to use.
For example, if you have the same logo at the top of every web page on your site, it makes it easy for customers to know what site they are on ("where they are" on the Internet). (Remember that many people will enter your site somewhere other than the home page, because they found a specific page on your site through a search engine.)
Linking the logo back to your home page also helps people find their way around on your site, helping them back to a familiar starting point.
So, putting your logo at the top of each page and linking it back to the home page are both best practices often seen on usable websites.
TheSiteDoctor.com uses a database of over 400 website usability best practices in helping you improve your website.