There is a bit more overhead when you can’t just overwrite a value in memory. But cpu time and memory space are some of the most cheap and straightforward resources to scale up compared to engineering time to resolve consistency bugs.

There is also a performance hit associated with mutexes or locking required to ensure mutable structures are updated consistently, and many high-scale systems have moved to append-only logs and copy-on-write semantics - structures that leave already-written data in place - because mutability/locking doesn’t scale.