The hard disk drive is not big enough to accommodate all your needs, such as software update/upgrade, install programs.
You cannot store more large files/data on it.
If your computer hard drive is full, it's likely that it will also have the following symptoms: Many users are discussing the topic regarding "C drive suddenly full" in Windows 7/8/10. Often times when the hard drive fills up, only the C drive is shown as full. In general, as the computer technology is getting more developed, hard drives always seem to fill up even when they are getting larger and larger.