Fuel saving? Flex takeoffs barely (if at all) save fuel, they reduce wear on the engines. Which is the significant cost saving here. The packs off allow a higher flex temperature.
Reduce engine wear?!? IF you can find one, please post [a link to] even ONE engineering study that quantifies the reduction in engine wear.
Once you get about 10% below max rated thrust, incremental reduction of engine wear is miniscule. Engine speed and EGT which are the main drivers of wear -- are already significantly below max. In fact, on the 744 and 748 we too often take off with thrust set SIGNIFICANTLY below climb thrust! That is simply a beancounters' exercise to reduce engine lease payments, and has NO operational value.