If you buy “fancy” coffee beans it doesn’t take long to notice how proud roasters are of the altitude (always in meters! Feet are for wimps!) at which their beans grew. I’ve never really cared nor understood how it mattered past being a marketing thing, until recently.
There are some rules of thumb when it comes to altitude and coffee. If you think about it, higher altitudes are harsher environments. The air gets thinner, the weather gets a little more volatile, there tends to be less shade, etc.
As such, it is thought that coffee plants put more “effort” into growing hearty, viable offspring (seeds, which coffee “beans” actually are) than their lower land brethren.
This tends to yield denser beans that tend to be more complex. Coffee that grows at lower altitudes tends to have it easy, so the plants get bigger and they don’t worry about pumping as much of their resources into their seeds, so the coffee at lower altitude (like most of Brazil, for example), tends to be less dense and less complex and the coffee plants yield more beans.
Certainly a lot of factors go into the final product that hits your palate, but the rule of thumb is higher altitude = potentially more complex flavors and depth in the cup.