I have two different recipes for poolish with equal parts of bread flour and water. One calls for 1/2 tsp. of yeast and the other only calls for 1/4 tsp.
Which amount should I use to make artisan baguettes and does it matter when I use the same recipe for other breads?
The amount of yeast you use heavily depends on your proving time, and vice-versa. You can use either amount, but your proving time will be vastly different. As highlighted in this recipe the fermentation time gets longer the less yeast you use.
Basically the yeast rises the bread, and the more yeast you use, the quicker it can get it done (like an increased workforce). This means you can use either amount, but you should adjust your proving times accordingly, and check manually whether you've gotten the correct proving result rather than use a set time limit.
Depending on how much time you have, most people would recommend less yeast and a longer proving/fermenting time, allowing for better gluten development and a deeper flavour.
