No a commercial food made of uniform bits is not the best thing to feed any animal. I don't care if it's your dog, cat, guinea pig, horse, or chicken. However not feeding them a commercial food means you have to balance their diet yourself. Being omnivorous chickens need a wide range of foods. Feeding too much of one food, not enough variety overall, or lacking in certain things chickens need to make eggs is going to cause more problems than commercial poultry feed. Most people's leftovers don't include enough protein or calcium to make a healthy chicken diet. It's also unlikely to have the full range of vitamins and minerals the chickens need. You'll probably be heavy in one food group or one specific food your family has a lot of. Even our diets technically aren't balanced for us. We add vitamins and minerals to things like bread, cereal, or drinks in order to keep us from killing ourselves through vitamin deficiencies. Unless you've done the research in to nutrition to include everything an animal needs in the right ratios you should not feed them without a prepared food. You'll especially have problems if you are feeding penned chickens versus free range. Some months out of the summer my free range chickens don't actually eat their poultry feed and they still lay plenty of eggs. Every animal should have supplements of fresh food in their diet. Even just cooking food has been shown to impact the diet a lot. Diets that could keep an animal alive on fresh uncooked food can cause early death and birth defects when those same ingredients are cooked. Another factor to consider with your leftovers. Again nutrients are added back in to foods like kibbles, poultry feed, or our fortified foods to make up for things like that. I don't think even dogs and cats should be fed without at least table scraps occasionally because variation in the diet provides both physical and mental health benefits. It's preferable you actually supplement your pet and livestocks' diets. You just want to do it in moderation unless you know you are giving them a balance of everything they need. Animals fed on balanced diets that include various foods without a commercial pellet/kibble may live longer but animals fed on only random table scraps these days are likely to die sooner. Leftovers here always get fed to something but what critter that is depends on what the leftovers are and what they've had recently.