Yeast nutrients tend to be in a more labile form than in wort, so the yeast can utilize them more quickly and efficiently. Also, wort can be deficient in zinc, which yeast need. You'll be fine without it, but if used as directed, you may observe shorter lag times.
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Primary: Brett Saison, Brett Berliner Weisse, sLambic I, sLambic II, Pils, Dunkel, Oud Bruin
Secondary: Flanders Red I, Cab Merlot
Kegged: Porter, Scottish 80, Pils, Orange Blossom Mead