I dont know about waste of energy it is a symptom of our grief and part of our emotions like any other , but i think its how we use it and get rid of that is important. Its energy but its turned into negative energy and we need to find a way to turn it back.Having a way to do that safely then prevents us from saying and doing something we may regret and also from further damaging ourselves.
I used to be very self destructive by internalising it - i would swallow it rather than express it in any way then dwell on it and conclude that it was my fault - sometimes it was of course, but in my world back then it was my fault every single time, and then you start hating yourself.
When you do that everything else is intensified - guilt, depression, anxiety, if you dont like yourself - why would others - so you reject them too.
also you dont care for yourself - whats the point of cooking /going out-/going to work to keep a roof over my head when i,m not worth it - every part of your life can be affected by it.