Is it true that it's only safe to drive with differential lock when you're driving in a straight line?

Question

I drive a DAF (division of Paccar) 95 truck. I transport sand, at the sandpit conditions are not always perfect. The other drivers tell me to engage the differential lock, but they tell me to only do it when you're traveling in a straight line (they say even the front tires should be facing straight forward) because you can damage the gears, is this true???

Answer 1

When the differential is locked the rear tires turn in unison. When you turn, the inside tire turns less and if the differential is locked either the tire will slip or the differential  will wear very fast or break.

Answer 2

The diff lock, the axles together.  When on pavement they can't "slip" to allow for turns.  This increases wear on the tires, makes turning more difficult, and eventually will end in a broke axle.

Answer 3

True? Basically yes.  Detroit locker/Differential locks in affect make a solid axle, no spin of one wheel in soft conditions but no turning  without wheel slip- acceptable in mud maybe.  Axles can twist and break, tire can be bad wear, steering very hard. Worst damage is trying to turn on pavement with lock engaged.