Upon shutdown, all running processes are sent a SIGTERM followed by a SIGKILL. The SIGKILL will follow the SIGTERM by an intentionally indeterminate period of time. Programs are expected to take only enough time to flush all dirty data and exit.
What it won't do is allow you to save your work in any open applications. You may lose work if you have any documents open, for example. But the filesystem caches should be flushed.