Anyone who's taken a project management course knows the monumental tedium of manually calculating start dates, finish dates, slack time, and other schedule values. Letting Project calculate a schedule is much more satisfying, so normally you don't want to place limits on the program's scheduling capabilities. From time to time, though, you need more control over task dates. Suppose the backhoe you need isn't available to dig the foundation until after June 1. A new database guru who starts work on October 12 probably won't start her tasks before that date. Or the trade show your company is attending takes place from July 8 through 12 whether your booth is ready or not.
The secret to scheduling with specific dates is the date constraint, or simply constraint, which limits when a task in Project either starts or finishes. Every task has a constraint, even if it's the completely flexible As Soon As Possible constraint.
For an easy-to-maintain schedule, keep constraints as flexible as possible. This section explains the types of constraints at your disposal and how to use them without forfeiting schedule flexibility. In addition, you'll learn how to use deadlines to spotlight key dates without applying inflexible date constraints.
Date constraints run the gamut from totally flexible to totally controlled, and each type has its place. Unless a task is associated with a specific date, stick to the most flexible constraints—As Soon As Possible ...