Hi Huckleberry,
More layers provide more flexibility to fine tune the comfort and support of a mattress both before and after a purchase as long as the layers can be re-arranged or exchanged. This can be helpful when it’s necessary and the flexibility of a design both before and after a purchase can be an important part of some people’s personal value equation.
You can read more about the different types of latex in post #6 here. The choice between Talalay and Dunlop is a personal preference and both are great quality materials that come in a range of firmness levels. You can read a little more about the difference in “feel” between them in post #7 here. Local testing on both when possible is the best way to know which one you prefer. Both types of latex in a suitable firmness level can be a good choice in either comfort or support layers for those who prefer one over the other.
Post #2 here has more information about the best ways to make comfort and design choices.
Phoenix