Yes, it is for specs after initial choice of say GLA. You then level and choose DRK. Then you are "rebirthed" as a DRK you keep some of your GLA skills and begin accruing DRK only skills. The primary reason for the splitting in my reasoning is the problem of 'never starting the advanced class from 1'. Yes, you mention that the skills will be "level 1" but it's only really in concept not actually in deed. I'd like to fight level 1 monsters, and have that old timey "thrill" of starting over.
It's honestly what I liked so much about FFXI. Being able to start over as new classes.