Flex
Flex thrust reduces wear-and-tear and increases engine life, but increases risk.
One measure of wear-and-tear is EGT drift – that is, the change of EGT compared to other parameters over time.
Benefit – I was once shown such a graph for a jet I managed. The previous pilot manager was not a fan of derate and the engineers showed me a trend-monitoring graph indicating wear-and-tear equal to six years' (derated) use in barely one year of operation.
Risk – I had a takeoff where improved climb thrust was erroneously (software design issue and human error) combined with normal speeds leading to low-thrust. I pushed the thrust up because it didn't feel right and we worked out the error later.