It does have its drawbacks. You noted that it requires arriving early and of course everyone has to do it to make any sense.
It certainly wouldn't have worked in the cases where my wife (who is notoriously late for everything) showed up. I've been at the checkin desk 30 minutes before an international flight and we got to the gate 20 minutes before departure, along with going to the head of the security line with a small child.
It probably does work to schedule to some lower-traffic airports with limited Customs hours, although they almost always get placed on call. I know over at Oakland International Airport, there are complaints about what happens when there's a delay. It's a smaller airport and they carefully schedule international arrivals to spread the load on Customs.
Huh?
Our local airport (Halifax) pre-clears for all US flights. So whether I am flying direct from Halifax to O'Hare or Boston or Newark or Orlando or any other US destination, I arrive 2 hours early and use the US departure area, clear customs in Halifax and go merrily onto my flight.
If I were to travel to the US via another Canadian city (like Toronto or Montreal) I would arrive an hour early and use the domestic departure area in Halifax as I would be taking a domestic flight, then I would more than likely clear customs and move from the domestic to an international area in the second airport.
I don't have a choice (once I have chosen my routing by buying my ticket) about where I clear customs. It is however greatly preferable to me to clear customs before my initial flight since it's no fun to run through an airport to do it if there is a delay in my original flight (BTDT!!)
Your wife would risk being denied permission to board by arriving at our airport that late. Not a risk I would take, but to each their own.
M.