Every job has its negative and positives. Whats more important while choosing a career in coaching is to make sure if you really have patience to train young players and have a believe in your ability to nurture young players into a better players. You need complete dedication towards your players to ensure they are learning and developing their skills as per your coaching. This can be taxing at times and requires lot of patience and general caring for the budding talents.
Not many negatives, being able to shape young players and ensure they are learning the game correctly and shaping them into better players and members of the community is very rewarding. The only negatives that I've seen is number of hours required and sometimes overbearing parents. If you can handle long hours and passionate parents, coaching is very rewarding.