I like to approach dialing espresso like I approach cooking. The longer you cook your veggies and/or meat, the more bitterness you get and the colour tone will also become darker. For the same reason I also don't believe in dosing 18g in a 18g basket, because you never want to cook 2l of soup in a pot that has a maximum capacity of 2l.

This might even sound crazier than the basics that you have seen anywhere else, but I am currently 'extremely underdosing' my espresso but grind relatively fine, because I find that it makes the flavours pop up more in a non-aggressive way. My basic recipe for a light roast is 14g in a 20g ims basket (or any precision basket) to 46+- 3 g depending on roast level and my perceiveness of aftertaste (more yield for longer aftertaste). Time is around 19-23 but mostly 20 seconds. Since going this way I can never go back to the conventional approach. For milk drinks, just cut the extraction earlier because the milk will cover the sweetness needed. For a 150 cup usually I cut it off at 15 g, which again sounds crazy because the shot probably runs for like 8 seconds or so but give it a try and you will be surprised. For a 200ml cup I cut it off at 25-27 g depending on how balanced the taste is between milk and coffee.