A user from Battle.net recently inquired about whether or not blood from battles could be kept on the ground indefinitely in Diablo 3. Bashiok was quick to respond with an initial explanation:
"Even decals, which are textures, impact performance. So there has to be some limit on how many of them are allowed to linger and for how long. We have to try to strike a balance somewhere. Also, a ground literally covered with corpses or blood becomes less and less interesting, more and more confusing, and can actually create some frustration.
Regarding visible markers, we put a lot of effort into building rooms and areas to ensure that the randomly generated dungeons are indeed random, but also not confusing and maze-like. We don't want everything to look the same. So in that respect a visual marker of a blood spot or corpse really shouldn't be necessary."
After some Battle.net users pushed for more details, Bashiok brought in Lead Tech Artist, Julian Love, to give a more detailed answer to their questions:
"Every independent thing that we show in the game has to be put into a special package that we call a "draw call," which is then delivered to the 3D card to be rendered on screen. It's not too different from preparing xmas gifts in that everything you want your relatives to receive must be packaged up in some way and then driven across the country in order to arrive there on time. Your CPU does this packaging and delivery and it takes a lot of bandwidth, so it ends up being one of the most crucial expenses to manage. Now, the truly horrible thing is that from a draw call cost perspective, each individual splattering of blood on the floor is every bit as expensive as a character or a dead body: they both cost one draw call. Beyond that, the differences tend to be somewhat trivial.
So, that's a lot of words just to say that blood splats can be every bit as expensive as, and in some ways, more expensive than dead bodies. It's counter intuitive, but this is the way it actually works."
Hopefully that clears things up a bit in regards to the issue of having graphics lingering on the screen indefinitely.