It is best practices to leave 10 GB or more disk space on an the SMP server's operating system drive. Many items can use the default OS drive rather than the install directory. These considerations should also be used even when installing SMP off of the OS drive.
Some of items to watch out for with low disk space are:
1. Package staging running out of room.
2. SMP and Operating system logging running out of space.
3. Pagefile expansion when managed by the OS.
4. Evenqueue processing.
5. Profiler and other diagnostics if saved to the users desktop or other areas
6. Windows temp folder growth.
There are many other possible problems that can be avoided by leaving plenty of space for the future.
Low disk space.
Leave 10 GB or more free space on the OS drive (c:).