Visual studio can integrate with an MS Team Foundation Server for source control and ALM.
A Team foundation Server organizes its data into Project Collections, which contain Team Projects. a Team Project may contain many visual studio solutions.
at work we have one Project collection, and each Team project is a full system we've built, containing one or more solutions.
Keep in mind, TFS is a seperate product so you need a seperate license to run it, and its a bear to install and maintain.
There are a couple reasons to use TFS, but the most important is the ability to control access to code by multiple developers. it controls checkins, checkouts, merges, and history/version control. These features can be valuable to a single developer as well, but as the name implies the general point is to enable a team of developers to collaborate on a system.