Some old recipes called for cans of extract, before you could measure it out exactly. In those cases you often see 3.3 pounds of LME, plus an amount of DME to make up the difference. Also, it could be that the person likes using DME at the beginning of the boil to reduce darkening or they like using it as a late addition to avoid having to remove the kettle from the heat as you would with LME to avoid scorching. There are a number of reasons.
Of all tyrannies, a tyranny sincerely exercised for the good of its victims may be the most oppressive. It would be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated; but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience. - C. S. Lewis, English essayist & juvenile novelist (1898 - 1963)