When/why would one use "vanilla sugar" instead of just plain sugar along with vanilla extract and/or beans/pods, particularly in recipes and baking? Is it just a matter of convenience?
I understand that some people might actually like to have vanilla sugar for direct use, such as sprinkling on things (as people also do with things like cinnamon sugar). I could imagine other "direct" uses, like flavoring coffee or tea with sugar that has a hint of vanilla. Besides convenience, in these cases having the vanilla already mixed in could allow quantities much smaller than would typically be measured otherwise in extract or whatever.
However, I've also seen an increasing number of recipes listing, for example, a cup of "vanilla sugar" in something to be baked. I can perhaps imagine a few cases where even the small amount of moisture or alcohol from extract would be undesirable (or something like that).
But aside from such unusual situations, when baking or making a recipe that has a decent quantity of sugar, are there advantages to the vanilla-infused sugar version compared to extracts or vanilla beans? Are there significant flavor differences/advantages to vanilla sugar?
Or is there some other reason it is popular?