In newspapers, the most important article is placed on the main page. If it is really important, then it is placed so that it can be found in the upper part of the first page - the lower part is usually folded and not always visible at first glance at the newspaper.
The same applies to browsers. Consider a button asking for donation on a non-profit site. If it is located far down on the page, you may not see it when you first look at this page. The user, of course, can scroll down, but many people will not do that and will skip the button altogether. For example, on the Google Earth download page, the number of downloads increased by 10% when the Download button was moved 100 pixels up. ')
However, browsers do not have a clear line separating the upper and lower parts, because different users may have very different monitor resolutions, browsers are not always deployed full screen and toolbars can take up additional space. In order to help you understand how everyone sees your website, a tool called Browser Size has been created. His work is based on a sample of google.com visitor data. Special code collects data about the height and width of the browser for a sample of users. For a given point in the browser, the tool can tell what percentage of users can see it. For example, if an important element is in the "80%" area, then this means that 20% of users have to scroll the page to see it. If you're a web designer, you can use Browser Size to change your page to minimize the need for scrolling and make sure that important parts of the page are always visible to your users.