Extreme case: V-drive world you typically see a big-ass tach on the dash...that's it. Not much to see or know there. I don't get it. Are other gauges so heavy they're an unacceptable compromise. Or just not cool? For that matter, why have a tach if other information about how an engine's running not important enough to measure. Is the dude with the big-ass tach gonna learn anything more than, "yup, that's how fast I spun it when all hell broke loose?"
No, If the big tach is used properly, you'll know prop burn RPM (cavatation), load rpm & Rpm at the end of your run ... the same things a jetter would want to look at.
As for me, I'm the worst offender. I have 3 guages ... the three that are important IMO. Voltage (that I don't really need, I know if my battery isn't charged ... the engine won't start), Boost, Oil Pressure. I have a playback Tach that I can't see while driving (mounted up in the gunnel). As far as the other data ... I have no need for it. That's why I have little to no gauges in my v-drive ... and why one should have a big ass tach.
Just my .02