Baking, I follow the recipe exactly the first time, then after that first time I usually tweak things a bit. Baking is much more scientific than regular cooking so the moisture, dry good, leavening all interact in specific ways so following the tested and proven recipe is important.
For every day cooking I "eyeball" things, although when I am following a recipe I do pay attention to quantities and sometimes actually measure.
When I am working on a recipe, meaning I am trying to record exactly what I am doing to reproduce it or perfect it, I measure carefully, write everything down exactly and then take notes on what to try or adjust next time I make the recipe.
I do have multiple sets of measuring cups and spoons and find them helpful. I'm a good home chef and helped with a local cooking school for a few years.