Just recently did a two month RTW holiday ex BNE. Scheduled on QF15 BNE-LAX, with seperate booking on AA LAX-SEA. Knowing that QF15 can be quite unreliable timetable wise, I made sure our onward flight to SEA had a good margin of error (about 8-9hrs), just in case. Especially as neither of us had negotiated LAX before. Turned out we were perfectly on time on QF15 so we had a nice ling wait in the lounges, but it certainly left me relaxed during the lead up to the flight that we had plenty of time in case of delays.
Continued this theme through the rest of the trip as much as possible, which meant no delays caused massive problems.
We did miss our flight DUB-LCY due to the bus running very late and security holding the other half up for quite a while, however BA rebooked us on to the next available flight to LHR. We were booked on the 1730ish Eurostar service LON-AMS that evening, but I made sure to book us on a morning flight from DUB, giving plenty of leeway, meaning we still had ample time to get to Paddington (after a couple hours plane spotting was conducted at LHR!) for our train. Only real disappointment was that we didn't get to experience the flight landing in LCY like i'd hoped.
I know there are times where it is hard to schedule in such delay margins, but it certainly makes things a whole lot less stressful when it can be done!