I don't know why people make such a big deal out of buying up lines.
It was done at both of my former carriers. Sometimes system form requires pilots at odd places and odd times of day.
Regional pilots fly "naps" all the time - late night leg out to an outstation, sit for 4-5 hours, fly the first leg back in the morning. Sum total block hours for the month were 40-50, so you got guarantee.
ACMI carriers too... on a long skinny international route, they may sit for two days at each city, waiting for the plane to make the circuit and get back to them. Never broke guarantee there either.