How often are you told that your project will start on date x and then it is moved to date y, maybe date z before it finally gets going?
Now when your project start date moves, you can just update the start date in the Project Information dialog and a lot of dates will update but not all of them (ex. deadlines, constraints, tasks with actual work). If you want those to move you need to go through Move Project.
The advantage of Move Project is that everything in the project is moved with respect to its original offset from the project start date. For example, in this project task b has a deadline 5 days into the project and task c has a constraint to start 2 days after the project’s start date.
Now I select Move Project to update the project start date to 1/12/11.
And everything in the updated plan has the same offset as it had before. Task b has a deadline 5 days into the project and task c has a constraint to start 2 days after the project’s start date.
In Project 2007 and earlier, you can access this functionality on the Analysis toolbar, Adjust Dates but there are a few limitations: deadlines and tasks with non-zero percent complete aren’t moved.