I imagine the most common question in discussions of creating animal-human hybrids is "why do it?" Julian Savulescu wrote an article for the American Journal of Bioethics addressing this question. He assents that there may be questionable motives - "commercial exploitation of 'freaks'; artistic motivation...or curiosity, just to see what it is like" (22). But he also discusses reasons that are more difficult to dismiss.
Medical purposes: Studying oncogenesis, as source of stem cells, or combining our genes with those of a species resistant to certain diseases
Delay aging or prolong human life: Could we incorporate turtle genetic sequences into our own to reduce telomere degradation?
Enhance human capabilities: Incorporate an elephant's memory genes, an owl's night vision, or a bat's ability to navigate in the dark.