Read push button switch status

I set up the simple sketch and wiring to read switch status but, my question is why is it not recommended to use an external pull up resistor. I used the INPUT_PULLUP, and it works fine but just wondered why an external pull up isn't recommended.

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Some sensors have built in ‘pull ups’ or ‘pull downs’ .

It is all up to you to decide what to do.

why an external pull up isn't recommended.

'cos the built-in ones are free, and don't require soldering.