Welcome, need2no,
I always wondered the same thing. If God needs nothing, why have people kill animals?
The JWs said that the sacrifices pictured Christ, and that the blood of goats and bulls had some atoning value. It never made perfect sense to me. One reason is because Abel made sacrifices long before the Jewish nation arose, and who told him to do that?
Of course, as a good JW I could not really delve into any questions that I had, lest I be thought apostate.
Isn't it nice to be able to have questions and ask them?