It is simply the footer where all the main information of the website is usually present.
Users tend to access the footer to get an overview of what the site offers in terms of products and/or services. The longer the page is, the more mobile users will have to scroll to access it and may be discouraged. Keeping the page height low therefore allows users to easily access the information they are looking for, improving their experience.
For optimal access, it is recommended not to exceed 10,000px. If the page height exceeds this recommendation, it is necessary to :