What is the reason for “locks are an expensive operation” to be uttered so often?

Question

I have read a lot of material on threading, and all the synchronization mechanisms involved. I also understand the dangers of not doing it properly.

I just watched th

Answer 1

Locks are often spinlocks, which cause a thread to "spin" doing no useful work when the lock is taken.

Doing nothing is expensive, since, as everyone knows: "time is money".