Tool life
How many pieces a cutting edge produces before it is changed, which drives both the perishable tooling line and the machine minutes lost to changing it.
Tool life is usually quoted in pieces per edge, and it decides 2 separate costs. The carbide itself, which is the price of the insert divided by its edges and then by the pieces each edge produces. And the machine time lost every time somebody stops the job to change it.
The second is normally larger than the first, which is why the cheapest insert is often the most expensive line. Halving the purchase price while halving the life doubles the number of tool changes, and the machine minutes outweigh the saving on carbide comfortably.
Predictability matters as much as duration. An edge that reliably lasts 380 pieces is more useful than one averaging 450 with a wide spread, because the first can be changed on a planned break and the second fails mid-run and usually takes a piece with it.
It is also a scheduling input. On a machine running unattended, a tool life shorter than the shift means the machine stops and waits for a person, which turns a 3 minute change into several hours of idle spindle. What perishable tooling costs per piece does the arithmetic on one operation.