WHY E CORES MAKE APPLE SILICON FAST

Summary from the TLDR Dev newsletter

Apple silicon Macs achieve their high performance mainly due to their Efficiency (E) cores, which handle numerous background tasks, rather than solely relying on Performance (P) cores. Immediately after startup, E cores are heavily used for processes like Spotlight indexing and initial backups, leaving the P cores largely free for user applications. This architecture is managed by macOS's Quality of Service (QoS) system, which prioritizes foreground tasks for P cores and restricts background tasks to E cores, even when P cores are idle.