A use case for the block chain is a tamper-evident log. That is, we want to build a log data structure that stores data and allows us to append data to the end of the log, But if somebody alters data that appears earlier in the log, we're going to detect the change.
If an adversary modifies data anywhere in the block chain, it will result in the hash pointer in the following block being incorrect. If we store the head of the list, then even if an adversary modifies all pointers to be consistent with the modified data, the head pointer will be incorrect, and we can detect the tampering.
Narayanan, Arvind, et al. (2017). Bitcoin and Cryptocurrency Technologies. United States: Princeton Press