in my case (Air Canada), its twofold: after spending $2000 on 2 one-way tickets home, I'd have to pay another approx $250 to select seats for our (2connecting) flights home. I refuse to. When I check-in 24 hours ahead I can pick from what seats are left for "free".(which I usually do). If they're all spoken for, at least I'll still have my boarding pass( AC is notorious for over-booking) so I'll have an assigned seat, but prob.in the last row!