I think there's some kind of weird mentality among web devs that client-size computations are free, but server-side ones cost resources because you do more of them the more users you have.
That’s not so weird. It’s like IKEA shipping you disassembled furniture: they don’t have to pay for assembly (nor for shipping as much air). The client bears the cost of assembly, so if you don’t pay the client’s costs, it’s free.