SuperD From , joined Dec 1969, posts, RR: Reply 2, posted (8 years 1 month 4 weeks 12 hours ago) and read 1797 times:
In simply "bumpy" air, it's perfectly fine. In heavy turbulence, it would probably not be recommended. It has to do with the load factor on the wings. In still air flight, the load on the wing equals the lift it generates. Significant turbulence can increase load factor. Banking does increase the load factor. Hence, the two together can be undesirable.
However, this is very significant turbulence we're talking about. With light chop, mild, or even moderate turbulence the load factor during a normal bank is nowhere near the airframe's limits. During heavy turbulence, such as inadvertantly flying into a thunderstorm with overhead bins popping open and people hitting their heads on the ceiling it would be advisable to keep the wings level. Obviously, airliners very rarely fly into these conditions where banking would be unsafe.