If you just enter the scene, you may not see the possible dangers surrounding your victim. For example, if there is an open wire and the patient is touching the wire whilst unconscious, it would probably be a bad idea to just enter the scene. Another example is, if there is a fire and you enter the scene, you may catch on fire. It is pretty much common sense, you'll survey the scene before you enter without even realizing it :). I hope this helps.
