Auto gearbox and clutch wear

[TonyN]

It's a bit like stirring a cup of tea with a spoon. So you can stay all day with a gear selected and the brake on. Nothing will wear out - but you will be doing work in the torque convertor and work = energy = fuel. If you drop into N, you will save a small amount of fuel.

Kev

But the ATF fluid degrades under load, so it won't last as long, and as has been mentioned, runs hotter, which also lowers it life.