The specifics here will vary for every organization, but the concept should be similar.
H: Just your stuff that nobody else should ever need to access. Example: your staff appraisal.
S: Anything that qualifies as “corporate data” which someone other than you might need access to, especially if you were to be unexpectedly away from your job for a while (such as being sick).
Important: A particularly bad place for documents: your desktop. Instead, put them on your H: or S: drive, but put a shortcut onto your desktop. Worth mentioning: email is also a bad place to save documents.
Computer’s C drives should be considered as mostly a place for programs, not documents. Sure, there are exceptions, but that’s the norm.