The Pentax Spotmeter V was used by Ansel Adams when he was developing the zone metering system. His fame from his landscapes of Yosemite National Park has cause generations of photographers to search out this light meter.
A spotmeter is an important tool, most commonly used by landscape photographers. The 1° angle of view makes it possible to take accurate exposure values of parts of a scene that are far away.
Medium and large format landscape photographers will often find themselves in need of a meter. I am not aware of a large format film camera with a built-in light meter. Many of the affordable medium format cameras do not have built-in light meters.
Without a light meter, there is no way to take accurate light readings so an exposure can be calculated. Using a spotmeter makes it easy to meter highlights or shadows, so you get the exposure you want for the darkroom or post-processing.
With modern digital cameras, a spotmeter allows the composition to stay fixed in place. The camera does not need to be moved around to use the spotmeter built into the camera. You'd want this for fast-changing light during a sunrise, sunset, or doing long exposures with an ND filter.
Review from: https://www.outsidetheshot.com/pentax-spotmeter-v-review/