How is it an advantage for the L1011 to not right itself?
It's because, while neutral roll stability (tendency to stay at a bank angle until disturbed) is an undesirable characteristic for an aircraft that is flying straight and level because more attention is required to keep it there, it's a desirable characteristic while maneuvering.
Normally, you have to choose one or the other, so you choose positive roll stability because that's the priority for an airplane designed to cruise.
Airplanes that spend a lot of time, or are optimized for maneuvering, like aerobatic aircraft and gliders, tend to make neutral roll stability a priority.  This is a really desirable feature on a glider that spends perhaps a majority of its time in thermals in 30 degree banked turns.  When you spend extended periods turning, the tendency to hold a bank angle is a great feature.
As well, when flying on instruments, a tendency to hold a bank angle naturally is a useful feature.  You are generally either in level flight where you want positive roll stability, or are in a standard rate turn, where a tendency to retain the turn rate without input is nice to have.
So, an airplane that had positive roll stability while level and neutral roll stability while maneuvering (on purpose) can be the best of both worlds.