Caution at all times!
There was the DC 10, operated by a large American company that recommended starting the tail engine just before take off. It seemed to be very sluggish on the climb out.
Fortunately the Manual covered in-flight starting!.
And with Viscounts: I believe it was the old British European that used to shut down two engines on landing to save fuel taxying in.
Unfortunately they changed from the 700 series to the 800 series and one crew still shut down the same engines.
One difference on the two types was the engines that supplied the brake system. Fortunately an RAF building in Malta acted as a standby system.
Personally, I have always been keen on saving fuel but not if it has required War Readiness power to be needed on the remaining engines to make a turn!