Hash functions are easy to overlook, yet they play a central role throughout modern software. Because they always produce the same short fingerprint for the same input, they are used almost everywhere identification, comparison, and verification are needed.
Git identifies every commit and file by a hash. Identical content produces the same hash, avoiding duplicate storage, while changed content produces a different hash, detecting the change. Blockchain also links blocks by hash, making it impossible to tamper with past records.
Hashes are used for deduplication (dedup) too. Comparing the hashes of files or data lets you quickly tell whether they are the same without comparing the entire content. Cloud storage and backup systems use this approach to save space.
Beyond these, the uses are endless — hash tables (a data structure), cache keys, content addressing (CDN), digital signatures, and more. Choosing the right algorithm for the job matters: use SHA-256 or stronger when security is needed, and a non-cryptographic hash when you just need speed.