Have used several browser fingerprinting services and have tried a few of the techniques myself, they're incredibly useful for fraud prevention when said fingerprint is reported against a central database alongside with the fraud that happened to _you_. The next time said fingerprint shows up at an eCommerce site, they'll be blocked off from purchasing or at least flagged for additional verification.
They could also be useful, in theory, for detecting session hijacking through cookie sniffing. Did somebody's device fingerprint change mid-session? It's possible that person's account has been hacked, so they should at least be made to log in again.
They're also just useful for super targeted ads.
shrug