When you edit an automation track and change the time for an event, you can turn on the Offset Following Events option to apply the same change in timing to all the events after the one you're editing. Otherwise only the event you edited will be changed. Does that make sense?
For example, if one event is a little off but all the others are good, you would edit that event but not use that option. If you wanted to insert an extra chorus into an arrangement, you would edit the next event after that section and change its timing by the length of the new chorus, and use that option to push all the subsequent events out by the same amount.