When and why would one infuse flavor into sugar for baking?
Adding herbs directly to baked goods usually results in very strong flavours. Infusing the sugar with the herbs gives a more subtle overtone rather than a full-on explosion. In some cases, of course, you might want a strong herb flavour, but where you just want a hint, infusing the sugar is great. The classic example is using stripped vanilla pods to make vanilla sugar, which adds subtle vanilla tones to cakes and meringues.