Too much nutrient at once is in effect, too much of a good thing. Yeast utilize the nutrients in different ways (and will require different amounts) at various times throughout their lifecycle. Too much too soon and you run the risk of overdeveloping the yeast; they will ferment fast and furiously for a short while, and then the fermentation will either slow dramatically or stick outright. In extreme cases, nutrients can even be toxic to the yeast. However, when provided with just enough of several essential nutrients (assimilable nitrogen being one of the most important, but not the only one) at different times throughout the fermentation, your yeast will meet or exceed their rated ethanol tolerance, as well as ferment more quickly and cleanly, producing fewer off-flavors in the process.
Lallemand here in North America have sponsored much research into the care and feeding of yeast fermenting wine grape musts. Several people here have taken the wine-specific guidance borne of their efforts and refined it to support the unique needs of yeast in a mead must.