@Mike: the end of your post is the key to this whole hobby (do you use the word "hobby"? I'm not sure it's right. A whole separate post on that subject, please, by each of you, T, B). You said "And even after you’ve booked your trip, keep an eye out for new space or other options."
My favourite trips are BR YYZ-BKK in J. BR releases J seats to/from Canada 10-14 days out. Sometimes they add more seats at T-24h. Wait until the very last minute? That's hard.
But it gets worse: with all its faults, Aeroplan offers two free stopovers on a roundtrip. That's a big benefit but there's a big catch. One must book homebound flights at the outset to qualify for a stopover. My tactic is to book placeholder UA seats in Y, then change to BR J when seats appear during my journey.
It's funny how different our psychology is about credit cards and flight bookings. By being very promiscuous about cards and very flexible (and confident) about flight availability, we get the goodies. Those who require stability and certainty pay more and/or ride in the back.