A fav icon is the small picture that is shown on the left side of the tab in your browser. This makes it easy for users of your website to find the tab with your website if multiple tabs are open.
Each time when a visitor browses a webpage from your website, the full page will be rendered - block by block. This costs time, while most of the pages remain the same for each visitor as there are no visitor unique elements on it.
When designing your website online in Webanizr there are four options for positioning each element: Default. Relative to other elements. Fixed within an other element.