Errors returned by expressions in SQL queries are not necessarily the same as the errors returned by equivalent PL/SQL expressions.

Have you ever noticed that error codes change depending on whether the context is SQL or PL/SQL?

DECLARE
    x number := 0;
    y number;
BEGIN
    select log(10,x)
      into y
      from dual;
END;
/

The PL/SQL block above returns following error:

ORA-01428: argument '0' is out of range
ORA-06512: at line 5

But if I change the way I assign the value to y, the error will be much more generic.

DECLARE
    x number := 0;
    y number;
BEGIN
    y := log(10,x);
END;
/

ORA-06502: PL/SQL: numeric or value error
ORA-06512: at line 5 

Now, this is a trivial case, but imagine a situation where you initially wrote the code in a certain way and then it turns out you have to change completely the approach for some reason, a business request, code refactoring, whatever.
If there is an EXCEPTION block catching a specific error, ORA-01428 for instance, after the change it won't catch that error any longer, presumably with some consequences for the final outcome of the procedure or function.