>>>Isn't that more of an issue of coding practices rather than using a variable vs defines? I can do the same thing you just said with variables.
>>>
>>Not exactly. If you define your constants in the include file, that's the only place where you would need to change them if used in multiple forms/programs.
>
>If I defined a variable in my main program as a constant (MY_CONSTANT = 10) then there is only one place I need to change it too. Just not getting the real difference here that actually makes a difference in development. I always thought they were something special, but they are just variables that dont change value. If I treat them as constants, then they are constants. What am I missing?

If you're using this MY_CONSTANT variable only in one program, then there is not much of a difference. If you want to have some common constants across the whole application, you may want to put them in the include file.