[FPGAhacker]

A closed lid MacBook will sleep unless an external monitor is connected. Amphetamine/KeepingYouAwake/Caffeinate does not change that.

[frankenst1]

    Closed-lid + External Monitor + Power Supply = awake
    Closed-lid + External Monitor + Battery = sleep
    Closed-lid + External Monitor + Battery + Amphetamine = awake

[acomjean]

Mine sleeps with the lid closed unless it’s plugged into power.

[fastball]

In what context are you using an external monitor without plugging your laptop into power?

[acomjean]

You could forget to bring your power adapter home and have some short tasks to do at home which benefit from large screens.