Why should I ever return something by value, since C++ features const references?

Question

Consider this function:

Thing func(){
    return something;
}

Every call to this function, a copy of something is made and passed

Answer 1

Because if your object (for whatever reason) was created on the stack of the called function, returning and using a reference to it is undefined behavior.

With return-by-value the compiler can sometimes optimize the return and there are no dangerous dangling references. With C++11 and move semantics this is brought to a new level.

It doesn't quite make sense to say "it's always better to return by reference rather than by value", each case where one is used, must be considered separately.