Why is SharePoint 2010 so widely used? I believe it is because it offers for the first time one technical solution that meets many business needs rather than just one.
If you want to improve knowledge sharing you will have many tools to consider. Again if you need to manage your documents you will have a wide choice of vendors. But if your business has more than one need or can see how solving one will create other requirements then a solution like SharePoint 2010 comes become more attractive to consider.
What if your organisation needs employees to use your intranet while away from their place of work? There are huge savings in office costs and increases in productivity if employees can use the intranet to help them with their work while they are mobile.