The App Router has matured significantly since its release. After shipping several SaaS products using it, I've developed strong opinions on what works well at scale.
Server Components are fantastic for data fetching and reducing client bundle size. However, they require a mindset shift. You can't just sprinkle 'use client' everywhere and expect good performance.
One pattern I love is using Server Actions for mutations. They eliminate the need for separate API routes for simple operations while keeping everything type-safe.
The biggest lesson? Don't over-abstract too early. Start with clear server and client boundaries, then extract common patterns only when repetition becomes painful.