In practice, you end up with apps which dynamically build up predicates in different sections of the code. And when you combine that with many predicates, many

In practice, you end up with apps which dynamically build up predicates in different sections of the code. And when you combine that with many predicates, many tables, and other constraints such as ordering or aggregates, things get complex pretty quick. Even if you have the best developers who understand all the in an outs of the dataset, re-implementing an optimizer in the app is rarely the right choice.