I use the deer fat when making burger and sausage. I like to keep it 100% venison. I know that by adding beef fat or pork fat I can make a blended product that will taste more like beef or pork... but that's what beef and pork are for.
When I'm feeling a little primitive I'll render some deer fat and use it for waterproofing boots.. and even for patch lube for my 50 caliber sidelock.
Richard