Really anything can be a good or a bad idea depending on the problem domain and how it's implemented. He doesn't really go into how he made it work too closely, so it's easy to say it was a success. The real interesting thing to understand would be, "Why was it a success versus other approaches?" What really made it a better choice vs other approaches? What was the team make up? He says that it made the code easy to understand. To whom? Interesting the team made it work, but not enough to say, "Sure let's try it without a lot more forethought."
Exactly! If you're writing a C compiler, it would probably be a bad idea to have that logic in a database, though it could be fun to try. On the other hand if your application is summarizing a lot data by different dimensions, it would probably be a bad idea to transfer all that data over the network only to summarize it in an application layer. Most applications have a little bit of both though and so will need both an application layer and database layer.
