You really care about exposing a serial number scheme for a list of books your company publishes, or the identifier for each of the various hotels you own, or the cities you have an office in or something?
Exposing a serial number can also be competitive intelligence. Number of users, transactions, etc.
Sometimes this matters.
It can give competitors the ability to estimate the size/success/etc of various aspects of your business.
This was a major motivation for a certain online retailer to generate non-sequential IDs.
Some other interesting examples in an old HN thread: https://news.ycombinator.com/item?id=7278198