Power exchange places one person in a submissive mindset. By doing so this can indeed be abused and cause psychological harm to that person. The amount of physical and mental energy a BDSM relationship takes can also negatively affect the dominant. Because this possibility of such negative effects does exist, the entire lifestyle can be considered edge play. This is why so often you will hear people saying that a solid self esteem is neccessary for those involved in BDSM. 

Those activities which are considered to be physical edge play are those which flirt dangerously close to permanent physical harm and/or death. Blood sports, knife play, breath control and needle play are a few examples of such activities.  

Many people seem to view these activities as some kind of milestone they have to reach. They see them as a goal for their relationship to reach before it is considered a real relationship. This is not true and in my opinion is a dangerous reason to attempt such activities. Not just physically, but mentally as well. A person could suffer extreme damage to their self esteem, if they find that edge play is not something they enjoy or a mistake is made and the sub ends up permanently hurt. 

For many, edge play brings satisfaction on many different levels. Mental, emotional and physical levels are all included. The knowledge, and ensuing fear, of being truly hurt can be an intense turn on for some people. The amount of trust such activities take  (literally placing your life in someone else's hands) is a heady feeling as well. This can bond the two participants even closer together. Often it is these emotional sensations that draw people to edge play. The intensity of a physical reaction during edge play activities can also be a major factor in a sadist's or masochist's reason for doing it. Physical pleasure and satisfaction are strong motivations.  

Edge play requires a great deal of knowledge, not just of your partner, but of the human body in general. You need to know where it is safe to actually do the activity and where it is not. You need to know the symptoms of shock, exhaustion and possible mental triggers. CPR and first aid knowledge are, in my opinion, a must for anyone in BDSM but an absolute neccessity if edge play is to be includewd. You need to know where the major nerves, artories and veins are to prevent damaging them or accidentally opening them in a knife scene for example. 

When I first began BDSM and heard of edge play activities I did not think I would ever enjoy them. But I have found as time has gone on, that I do enjoy them. I started with light breath control and enjoy that immensely. I hope to try different things in the future. For me, it is the combination of the mental and physical sensations that draws me to edge play same as it is for many others. Edge play certainly is not for everyone, but to me, so long as it is consented to by the participants and done as safely as possible, it is not my place to say whether it is right or wrong. Nor do I consider that those who engage in edge play activities are somehow better than those who do not (or worse than for that matter), I think it is just a different side of the same coin.  

Play safe and Enjoy!