Hotter water pulls flavor faster. That's the whole rule. Everything else is matching the temperature to what you have in the bag.
Roast tells you the range
Light roasts are dense and closed. They want hot water — 94–96 °C — to crack into the fruit and florals locked inside.
Medium roasts are forgiving. 92–94 °C extracts most coffees evenly. Start here when you're unsure.
Dark roasts are already developed and fragile. 88–92 °C keeps you from pulling out ash and char on top of the roast flavors that are already there.
The off-boil shortcut
If you don't have a thermometer, boil the kettle, lift the lid, wait 30 seconds. You're somewhere around 93 °C. Good enough for most coffees. Adjust by feel from there.
At altitude this math breaks. Water boils at ~92 °C in Mexico City, ~91 °C in Bogotá. The "off-boil" trick already starts below the spec, so don't wait — pour straight off the boil for light roasts, and skip a degree or two for dark.
When the cup is wrong
A bitter, drying cup at 96 °C might just be too much energy for that bean. Drop a couple of degrees before you blame the grind.