[fizzbuzz-rs]

Likely because the hash of an IP can easily be reversed as there are only ~2^32 IPv4 addresses.

[openplatypus]

It is not just that. Having user IP and such a hashing approach you can re-identify past sessions.

[thih9]

What if my hashing function has high likelihood of collisions?

[firtoz]

Then you cannot trust the analytics

[rjmunro]

You can estimate the actual numbers based on the collision rate.

Analytics is not about absolute accuracy, it's about measuring differences; things like which pages are most popular, did traffic grow when you ran a PR campaign etc.

[thih9]

Do you trust analytics that doesn’t use JS? Or relies on mobile users to scroll the page before counting a hit?

It’s all a heuristic and even with high collision hashing, analytics would provide some additional insight.