Is the bigger the C disk space of the computer, the better?

No, there's no harm in being too big. It's just a waste of space. Generally speaking, the space of drive C is allocated according to the system version. XP is generally 10G, which is enough. Of course, most people don't install anything else on the C drive, just install the system. If it is Vista or windows7, the C drive should be allocated a little larger, because the system itself takes up a lot of space.