The single leg deadlift is not about where the leg goes. It is about where the hips and glutes go. It is a part of walking, running, and hip extension. If you don’t know how to load it, you can’t extend it appropriately.
The hips and glutes move back and when done correctly, it does not matter so much where the feet end up.
Don’t be a flamingo or a tippy bird. Do the movement correctly and get the most you can out of it.
If you just kick the leg out there is a possibility that you will flex at the lumbar spine. That can set you up for a potential injury and knock you out of training.
The SDL is a often used piece of our rehab and training programs.