Sifting makes sense if you knead by hand - makes absorption easier.
Toasting spices in a little oil - spices release flavor into the oil and your kitchen smells awesome.
Meat also releases fat when browned. So it is kind of self sustaining.
Whether you dry-roast or toast in oil depends on what you're trying to achieve; if you want flavoured oil for something like a tadka, then you use oil. Dry roasting to season e.g. a curry produces different flavours. It's also harder; different spices burn at different speeds, so for example add cumin first and turmeric last. burnt turmeric is very bitter.
