Do dishwashers clean dirty dishes better than clean ones?

[strawbridge]

An acquaintance recently told me that her appliance repairman advised her that she should leave some food residue on dishes she puts in her dishwasher (instead of thorougly pre-rinsing them) because it would cause the dish detergent to be more effective. Something about the detergent needing some grease/oil deposits to "work against" and suds up. Has anyone else heard this and does this really make sense?