The concept of trust isn’t one we think about with simple applications such as this one, but it’s there nonetheless. In a conventional web app, the job of accepting or rejecting my recordings would fall to a centralized server (or cluster of servers, running identical code), which would have similar logic as above. However, there are plenty of use cases for blockchain or distributed ledger technology, where relying on a central authority is dangerous.
DAML offers us a set of tools to solve problems like this explicitly and conveniently. While there would be nothing wrong with using a single “operator” party for all users of my habit-tracking application, I know (and my users know) that we have the option to switch to a distributed model in the future.