I haven't set a preliminary inquiry and then waived it at a later date in recent recollection. I'm sure I have at some point, but that's not a common occurrence. That's because court time is so precious. When we're talking about the root causes of delay—why does it take so long, in some cases, for matters to be heard?—part of the answer, I think, is disclosure, and part of the answer is the legal aid process, but most of it is getting court time. That's the longest delay.
I have clients in custody who I think should have a preliminary inquiry. It could focus the issue and it may be beneficial to them, but they still don't want to set up a preliminary inquiry because it will delay them. It's very rare that a preliminary inquiry will be set and then waived. Even when it is, at least in Ottawa we're double- and triple-booking our courtrooms, so if a preliminary inquiry is set and then waived, at least in this jurisdiction, there is a trial to fill in that time.