When is Pantone color used over CMYK color?
Ideally, the proper scenario to use CMYK color are for full color images such as photos and produced/edited pictures via Photoshop. The reason for so is becuase CMYK ink is simulated (not mixed) which means that as an image is printed, thousands of dots of either to all of Cyan, Magenta, Yellow and Black color will compose an image as originally rendered in raster graphics (graphics that are pixelated, not smooth which furthers the need for dots to be used to replicate the rasterized image). Pantone colors, on the other hand, should be reserved for designing logos and banners (usually from Illustrator).
The reason of this is solely because Pantone colors are mixed, unlike CMYK colors, and offer palette swatches to a user in which a color can be selected to produce blended and consistent color tones (from true blue for example to its numerous shades such as colbalt blue and teal). Applications that require Pantone colors need it for the profession of presenting neatly and smoothly (the latter, coming from vector graphics). Lastly, CMYK colors are less expensive than Pantone colors and additionally, Pantone colors offer more variety as aforementioned in color swatches which increases the value of when to use it (mainly for professional graphic design applications).