I believe having a strong baseline schedule is really important. Scheduling seems to be easy but it is never hundred percent accurate. There will always be unexpected events that can throw a team off schedule. For example, one of my coworkers was having trouble for one of his projects, the quality department was taking to long and signing off documents on time. They had to make contingency plans in the meantime however they could not move forward without the signatures. This is one way your schedule can be disturb. There are somethings we can control.