I use blood from animals I butcher in the compost or directly in the garden. It's a great addition to soil. A couple years ago I spilled some blood on the lawn: for the rest of the summer you could see a small patch of grass that was thicker and healthier than the surrounding lawn.
If it's fresh, you can dilute it with water and then apply it to your garden soil. You can add it to your compost pile if there's too much to use on the garden or if it's out of season. I suppose you could dry it, but that might be more work than it's worth. Depends on how much blood you're dealing with and how much area you have that could use the nutrients.
I can't see a downside, except if there are wild critters in your area that might be attracted by the smell of blood. Raccoons, skunks, opossums, bears, foxes, cats, coyotes, vampires, werewolves. Probably not those last two, but maybe some of the others.