Actual animal-meat burgers don't literally have blood in them. They have myoglobin, which is similar to the hemoglobin found in blood, but different. So a burge

Actual animal-meat burgers don't literally have blood in them. They have myoglobin, which is similar to the hemoglobin found in blood, but different. So a burger doesn't bleed, it has moisture which makes it wet and myoglobin which makes it red, but the red liquid isn't blood. Anyway, there are 3 purposes I can think of: (1) Looks. The myoglobin substitute, leghemoglobin, that they put in the Impossible Burger will make it look more like real meat, which will visually appeal to people who like meat. (2) Flavor. Myoglobin also affects flavor, so again a more realistic imitation of meat. (Incidentally, apparently myoglobin content is the main difference between dark and light meat chicken. Myoglobin stores oxygen, so muscles that get used more need to contain more of it. Since chickens walk way more than they fly, chicken breasts have little myglobin whereas chicken legs and thighs have more.) (3) Nutrition. Myoglobin contains iron. People always talk about vegetarians getting enough protein, but iron might actually be a bigger challenge. And heme iron (as found in meat's myoglobin and in Impossible's leghemoglobin) is easier to absorb than non-heme iron (as generally found in plants).