I am using a message map with a custom ON_MESSAGE handler. The callback function called by the message handler requres the return type to be LRESULT, but I am not clear on understanding what I should return in the LRSULT, and how the return value is used.

my callback function called by the ON_MESSAGE call in the message map calls a function like:
LRESULT ClassName::CallbackFunction(WPARAM wParam, LPARAM lParam);
and I have found many examples online that return "LRESULT(true)" from this function, but little explanation of why return true. Could I/Should I return other values ever? What does this return value get used for?

MSDN's explanation that LRESULT is the "Signed result of message processing." and is typdef'd from LONG_PTR doesn't give me the insight I was hoping for. Thanks for your help!