Your advice is good, but the spirit is wrong. They do that to save fuel not just to cut costs but also to reduce consumption, which is net positive if you factor in environmental conerns. Some locations require it for noise abatement. Also, reducing the wear on the engine means more cycles and less maintenance/chance of engine damage. These parameters are well tested and are very well understood. Planes take off at mere 150kts, compared to what their cruise at, which is more than 250 knots. If you can take off at lesser thrust, it's not bad to do it. It's not like Airlines are making huge profits out of it too.