Higher temperatures extract soluble compounds much more easily than lower temperatures.

For espresso, where the contact time is very short:
Light roast brew temperature Celsius is 95 degrees.
Medium roast brew temperature Celsius is 90 degrees.
The dark roast brew temperature Celsius is 85 degrees.

Your coffee is likely to be roasted somewhere between these extremes. The optimum temperature for your roast level will fall somewhere on this scale.

Using the right temperature for the Roast Level, as the density indicates, helps get the extraction right.

Interestingly, the mid roasts, which fall around 0.390 g/ml, require 89-90c, somewhat below the SCA recommended 93c. People are waking up to the fact that mid-roasts taste better at a lower temperature than people have used in their fixed recipes. You can see this in many winning AeroPress competition results.