There's a worse problem, which I've seen in the wild:

    int some_function(...);

    int some_other_function(...)
    {
       int r = -1;
       /* imagine a bunch of other locals defined here */

       r = some_function(...);
       if (-1 == r)
       {
           return -1;
       }
      
       ...
    }

Now imagine someone changes the return type of some_function():

    char *some_function(...);

    int some_other_function(...)
    {
       int r = -1;
       /* imagine a bunch of other locals defined here */
       char *s;

       s = some_function(...);
       if (-1 == r)
       {
           return -1;
       }
      
       ...
    }

Oops! Every other reference to r has been removed except the declaration and the test. Now some_other_function() will always take the early exit, and because r is initialized in its definition the compiler does not complain. (In real life, hilarity ensued.) If it was 'int r;' with no initializer this would have been caught by the compiler.

Modern gcc is great at finding uninitialized and unused variables. -Wall -Wextra -Werror FTW.

EDIT: referred to some_function() where it should have been some_other_function().