I taught my project dashboard workshop today. One of the things most people want to measure is progress towards project completion. But you can't measure project completion progress unless you have completed features: developed, integrated, and tested features. A completed feature is done enough for someone to use.
Implementing by architecture leaves all the feature integration up in the air until the end of the project, so if you must implement by architecture, you just can't measure completion until the end. That's too risky for me. But if you implement by feature, you can start measuring completion as soon as you've implemented one feature.