Why do you prefer that a function (member of an object) not return a boolean value to the calling function in order to indicate that it (the called member/function) successfully completed its operation.

Like mentioned in the question, it isjust a preference and not a rule. It is a commonly accepted way ofdoing OOPS methodology. There is nothing wrong with returning a boolean value but it is not PREFERRED. Hence refrain from it. It is preferred that the called function/member throw/raise an exception to indicate that something went wrong in it. Again, this is just a preference and there is nothing wrong in doing it. If you do choose to use it extensively, you are moving away from doing Object Orientation or Object Oriented Programming.