Bill Hunt answered both your questions. The reason for keeping vital info, such as text in Title Safe is to accomodate virtually all display systems, including those with overscan and those without... old and new. You rarely know with a projection system whether the entire raster is being seen, or if there's overscan. It depends on the venue, and often the person setting up the projector.
Think of Title Safe as the Lowest Common Denominator.
I did a convention video last year, where the company doing projection assured me I could use the entire raster. That video was only going to be seen one time in one theatre. So, I was able to put the text all the way to the edge. But, that's something I'd never do if I was going to send DVDs out into the world, where every TV is different.
Eventually, the client asked for a DVD to distribute. So then, I took the project into Ae, and squeezed the original raster to just inside Title Safe, and left a black border on the sides. That way, I knew that Granny Oldschool with her 1952 RCA would be able to read all the text just fine.
There's nothing to prevent you from doing multiple versions for different venues, but how do you know if your audience will choose the right version, if you're not there to oversee the screening?
