Sharing files and folders with Vagrant machines is a typical use of Vagrant in a development environment. Files on a host machine can be shared with a running Vagrant machine, giving developers the advantage of being able to execute code in a production-like environment while having the ability to use desktop productivity tools (IDEs and text editors) to modify code. There are some cases where sharing folders between a host and a guest might not be possible, or might not perform well for the task at hand.
Two possible examples are:
Processes that generate significant disk activity (I/O) on shared folders: Hypervisor folder sharing (particularly VirtualBox) can cause Vagrant processes to become I/O bound. Using NFS can help, but might not always be available. (Exporting NFS shares require root access to the host machine and in a few cases, it might not be available at all.)
Vagrant can be used to control virtual machines in remote locations (even in remote data...