Demo trading has diminishing marginal productivity. After a prolonged period of paper trading, a demo user creates his/her own reality of trading, rules and observations that are not always applicable in real time trading. Some people have spent so much time in paper trading that once they move to real trading, they halt their trading upon the smallest of obstacles. Sadly, then they go back and forth between the two, without any significant improvement.
If someone starts the journey of demo trading without knowing the psychological and execution limitations, it becomes a futile exercise.