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Why do MacBooks need power cable when it connects to external monitors
and why can they not put display off without closing lids ?
If you are Windows user, you might not know this; You cannot turn off the laptop display when you connect MacBooks to external monitors.
The only option you have is either to mirror the display to another or using as extended desktop

When I use external display connected to my laptop, time to time I’d like to keep the lid of the laptop open especially when I do heavy-duty work such as video editing. Because by design, laptops has quite severe limitation of heat handling. Keeping the lid open makes the head issue a bit better.
At the same time, I’d like to put the laptop display of to save some graphic power of my poor old laptop. But I cannot !
I see Windows can do by one-click (or maybe a couple of clicks) ?
Nobody in Apple.Inc did not express that it is inconvenient ????
If you are Windows user, you might not know this; You cannot plug off your laptop while you connect your laptop to the external monitor and…