In the past I have generally added my spices to the oil in the early stages of a main course. This seems to be the common way. I noticed in some of the base sauce recipes that the spices are added in the "water" stage.
Is it just preference/ease or does it make a difference to the base or main dish?
I think that it must make a difference. If added to the oil, the spices will fry; if added to the "water" (sauce), they will braise but they can't fry. Before I discovered the BIR style of Indian cookery, I followed the traditional recipe books and always fried my spices; now I am converted to BIR, I braise them, and (purely personally) I prefer them braised. But there are many experts on here who will swear by frying them, and so it must be possible to get as good, if not better, results by frying than by braising.
** Phil.