How does the As Soon As Possible (ASAP) constraint affect my project schedule?
Project Central uses constraint type rules, along with work durations and dependencies, to determine the scheduled start and scheduled end dates of work items in your plan. With ASAP selected as the constraint type, the start and end dates of items will be as soon as possible, given the current date, duration, and dependencies. This article describes how the ASAP constraint works.
Note: The ASAP constraint allows the scheduler the most flexibility to adjust the schedule, so it is recommended that you use ASAP for most work items unless some other constraint is specifically needed.