Depends what's the situation, but I usually try to write realistic details that would show the reader an image his dirty mind would fill out. For example, if someone got decapitated, I'd write that his head flew away, rotating in the air and trailing blood. Generally I try to avoid unnecessary gory details - there's (usually) no point in describing how someone's innards fall out of the hole in his stomach. All I need is the fact that it is happening, and the reader's mind will do the rest.
Though in some cases, when the character's attention is focused on what's happening, it's good to desribe the details to emphasize that the character is paying attention to it and is feeling strongly about it.
In the end it all boils down to the character - if we're in the middle of a quick, action-packed brawl, I write a short, concise description, but if it is, for example, a tense moment after the fight when the character is inspecting their wounds, a more detailed description would be expected.