Yes it’s for replacing all the fans, or for bulk applications

I have five fans in my case: 3 on the intake/CPU radiator, 2 top exhaust, and 1 rear exhaust. Seems pretty standard for a midsize case.

The case fans that came with the case were just okay so I upgraded and could have used a 5 pack product.

I don't think fans fail that frequently that you need to buy extras for replacement beforehand.

I just built a PC, replaced all the Fractal stock fans with Noctua ones. If you need a never been used stock Fractal fan 140mm size let me know and we can work something out?

Some cases can host much more than 2-3 fans. My old but reliable CoolerMaster ATX case can host up to seven 120mm fans. I don't need that much for the light gaming I do but for some people, it's cheaper to buy them in pack rather than individually, either for a single build with lots of fans or if you are building computers for a living.