The point is that you can have a prototype "void|<something> func();", which can be implemented either by a function "void func();", or a function "<something> func();" (type restriction). So if you don't need the services provided by returning a <something>, you can write
void func() { code code }
instead of
int(0..0) func() { code code return 0; }
which is shorter and more to the point.
You've only shown it if one chooses to accept your argument.
The argument that simplifying for the end user has value, yes. If you do not agree with that argument, then I don't suppose we have anything further to discuss.