Design: Signals => Pass by Reference

[wysota]

What argument can stand to eliminate all of these benefits?

If we connect two (or more) slots to the signal and both of them change the value, we lose one (or more) of the changes and only the first callee receives the original (unchanged) value.

To counter your upcoming argument that you are going to connect the signal to only one slot -- if you know who is going to be the receiver of your signal, you don't need a signal at all. Instead call the method in the receiver object directly. This will be even faster and less complex than using signals.