I intend to offer something sweet with each meal, but it will be fruit- probably unprocessed fruit- and it will NOT be an incentive for finishing a meal.
In terms of maintaining a healthy weight, cleaning your plate every time you sit down is actually a very bad thing. Eating more than you want to get additional food that you want because the consumption of food has been tied in with the reward center in your brain seems like a recipe for obesity to me, and while I'm only very mildly overweight myself (I am pregnant and have suffered...every complication I'm familiar with, so far, and have been unable to exercise), I have struggled with overeating most of my life.
The way I see it, by putting fruit on the child's plate and allowing them to eat it at any point during their meal not only teaches them to eat healthy sweets, but makes sure that they get enough fruit and doesn't teach them to eat everything they're offered just because it's being offered.