Over time, you get used to where all the gauge needles should be and it becomes easy to notice if something is out of place. The AAA gauges, Attitude, Altitude, Airspeed are the most important, and also the ones that change a lot. Something like EGT or the voltmeter is just for diagnosing error conditions. A warning light will turn on if one of these values gets out of wack.

Numeric displays require a lot more conscious effort to read a number, decode it , decide if it is an acceptable value. This is why the steam gauge style remains popular, even if it is a digital render now.