"It Increases fuel burn.
Strange, but true. This is because:
1. Assuming an uninterrupted climb, it will take longer to reach the more economical cruise altitude than a full thrust climb.
2. Engines are less efficient when not at full thrust. "
To address each point:
1. On a snapshot basis, I have to agree. However, if you routinely employ reduced thrust, your engine fuel burn remains closer to a new spec, and thus the long-term effect is a trip (and fleet) fuel savings. (It's not only EGT we're preserving, but fuel burn as well)
2. Not all engines are really "less efficient when not at full thrust". The best modern engines actually have an SFC "bucket" or J-curve i.e. most efficient at cruise.