A few guidelines:
Best for Blenders
Whipping up smoothiesBlending frozen cocktailsEmulsifying vinaigrettesPureeing dips and saucesStirring cake or pancake batterLiquefying soupsBlending spreads
Best for Food Processors
Stirring thicker mixtures, such as cheesecake fillingChopping vegetablesChopping nutsMaking pestoMincing herbsMaking bread crumbs or graham-cracker crumbsGrating Parmesan