hardly a dumb question.
the answer is "practicality" and "need"
I'm another one that has largely converted to weighing ingredients - not only for the typical bread baking, but pancakes, rice, water, sugar, shortening, etc.
it's just easier, for me. and like Guts, I simply weigh them the first time around, make a note on the recipe card/paper/book, then make a note of any adjustments needed - ie increase/decrease - as I go along. after 2-3 trips it's pretty accurate, fast, very repeatable and reliable.
small qty stuff like teaspoons/tablespoons one can weigh - some folks have a separate highly accurate scale just for small quantities. frankly, I just wing it - pinch/fat pinch of salt, spoon of yeast, ground pepper - gosh don't think I've ever weighed or volume measured it - I just grind away until it looks right . . . (most seasoning are 'to taste' anyway . . .)
like yeast - a little more or a little less rarely makes a difference - a tenth of a gram (for example) is actually not significant. it may affect the rise time by a couple minutes - but you've probably noticed most bread recipes are "until doubled" and frankly judging "doubled" is very subjective and secondly the ambient/rising temperature plays a lot bigger role than variations in yeast quantity.
I have my exceptions - liquid flavorings / extracts - yup, I have measuring spoons and I use them.
a new recipe . . . this is not a good opportunity to "wing it" - I measure and follow the recipe. then I decide if I like it or if it needs more/less x,y,z.
I don't have a problem using grams of flour and half-teaspoons of vanilla extract, for example.
the "need" basis for accuracy has any number of variations, but one common issue is scaling up a recipe. winging the amount of salt / baking powder for a 3-4 people batch of biscuits is one thing. if you get tasked to make your famous buttermilk biscuits for a crowd of 100, those small winging it errors can produce a catastrophe when multiplied by 10's / 100's.