It has value in a PHEV. Here's a photo from my PHEV, with labels describing what's shown. This is a much-better-thought-out instrument panel than is what is in Toyota Hybrids (and Primes, from what I can see), as it's very clear and really let's the driver know what's-what. Note that the gas tank is about 88% full, even after driving 290 miles of local driving (since my last fill-up on gasoline, some three weeks earlier) in which I plugged in every night in my garage, and the computed fuel consumption over this range was 98.4 mpg. This is why we are excited about the RAV4 Prime, with nearly double the range of my 2018 PHEV, but I wish that the Toyota instrument gauges were more practical and useful to the driver.Seems the problem is that the tach really has no value as we move toward an EV world.
Below is what it looks like when I'm in all-electric mode and braking, so that the regen braking is charging the battery (lights at bottom light up to the right side when the battery pack is charging). Yes, it's possible to both charge the battery pack and use the battery pack for power at the same time, also. The photo below was taken at night, so you can't see the E-POWER and CHARGE labels at the bottom of the dial. The tachometer is a regular analog tach, but the rest is digital.
And below is a daytime photo of the tach in my PHEV when driving with the engine on (and electric motor off, as the engine here is charging the battery pack at my direction):