> Then I put a breakpoint at that line and hit f5 and don't try to guess what may or may not happen because in the end that's the only way to know what actually happens

There's no need to guess if the parameter is passed by value only. When pointers are used visual inspection alone is enough to ensure that the reader knows what he value of the argument is after the callee returns.

I said that it's easier to read when pointers are used, and you propose stepping through the code as an alternative. Surely you see my point now?

You can't always reproduce a bug. Also, do you Step Over do_something(x) or Step Into? You definitely step into if it's do_something(&x).