The two main uses for const are to declare large compile-time initialized tables of information as unchanging, and to specify that pointer parameters do not modify the objects to which they point.
The first use potentially allows portions of the data for a program to be shared by other concurrent invocations of the same program. It might cause attempts to modify this invariant data to be detected immediately by means of some sort of memory protection fault, because the data resides in a read-only portion of memory.
The second use of const helps locate potential errors before generating a memory fault. For example, functions that temporarily place a null character into the middle of a string are detected at compile time, if passed a pointer to a string that cannot be so modified.