Do you need a long landing page? It really depends. There are times when a long landing page is beneficial, but generally speaking I’d say a landing page doesn’t need to be any longer than it needs to be.
In some sectors, a long landing page can be beneficial. Financial analysts, for instance, like lots of figures. So if you are asking for thousands of dollars in investment money and you expect to close the sale then you might need to provide a great deal of information in order to satisfy the needs of your target audience. With other sectors, that long landing page and minute details could be detrimental. It behooves you to know your audience.
But it’s more than just target marketing too. There are other factors that should determine the length of your landing page. What are you asking for? If you are just asking for subscribers to a newsletter then your landing page doesn’t need to be that long. If you are asking for a big commitment or a long-term commitment then your landing page might need to be longer. However much detail is necessary for a person to make a reasonably informed decision should be your guiding principle. If a good decision requires lots of information then maybe a long landing page is necessary.
The agreed length from a marketing stand point, especially talking squeeze pages is above the fold. In any case all your best points should be above the fold and that fold occurs at 1024 resolution.