Animal sacrifice in my eyes (and I have every right to think this way, and reason) is for those who lost (or never truly had) the ability to do decent workings and so they hope their gains comes from killing something instead of them actually succeed in something out of their own.
My Satanist ex thought it will get his curses casted by his cult done on me, until he got wrecked by Lucifer and me for being an idiotic clown who imagined performance and power behind blood thrown around like a lunatic. It cost him his job, his parents, his peace and stability. His sacrifice worth nothing.
Let's approach this from an another perspective. People love giving offerings for many reasons. Let's put aside the bond building out of pure intent and love, and focus on the most common reason; gains. Because for many people, these are simply bargaining chips for results. They believe, the 'greater', the more abundant the offering, the better the result. Offering foods, minerals, incense, oils or things like artistic works made by your own hand does not always feel satisfying for everyone. This is where focusing on life essence comes to the picture; be it blood, or a life.
Truth is? What can be achived 'with blood' and 'animal sacrifice' in magic, can be achived without it. No exceptions. Like it or not.
Sacrificing a living being does not differ much from any other sacrifice, you just offer more is all. It's still up on you and the judgement of the spirit.
Also, here's a thing: in my eyes SACRIFICE is giving something you love, and appreciate, something that does matter to you.
If you throw anything into the way of a spirit for result you have no decent bond with, it is not a sacrifice. Just an offering.