Hi BobinCA,
The height of a pocket coil is just one of many variables that will affect the feel and performance of the coil and how it responds to pressure and how well it can contour to the shape of the body. Some of the others include the gauge of the coils, the number of coils and the coil diameter, the number of turns in the coil, the shape of the coil (cylinder, barrel etc), and the specific design of the coil (single spring rate, multiple spring rate etc).
While it does affect the performance and response of the pocket coil and the mattress “as a whole” … there are also marketing and financial considerations involved as well because many consumers believe that thicker mattresses are somehow “better” and as you mentioned some mattresses that contain taller coils that can contour to the shape of the body more effectively may need less padding materials above the coil as well.
Having said that … I would keep in mind that an innerspring isn’t normally the weakest link in a mattress and the useful life of a mattress will depend much more on the types of materials or components that are on top of the innerspring than the innerspring itself. A “better” innerspring is always relative to the specific needs and preferences of a particular person and would be the one that is part of a mattress that is a good “match” for you “as a whole” in terms of comfort, firmness, and PPP (Posture and alignment, Pressure relief, and Personal preferences) so the height of a coil wouldn’t be particularly meaningful in terms of assessing the durability or useful life of a mattress. There is also more about the pros and cons of different types of innersprings in this article and in post #10 here.
Phoenix