Yes thats one use, things like a version_number constant, so instead of having to dig though the source code and change each place the version number is used, you just change the constant. But another common is use for bitflags, which is easier to remember,
the_options & option_1 (checks if option_1 is set)
or
the_options & 0x0001 (checks the same thing)
Making option_1 a constant that = 0x0001 makes it a lot easier to work with since you never have to worry about forgetting which bitflags represent which values. There are also a couple other uses, for example some programs have a constant called "debug" which is set to false, but simply changing that one line so that debug is true enables debugging. Thats very helpful since you can have your release version without the debugging code, but only have to change one line when you want to reenable it to make sure it works.
