When my children were young I felt inspired (yes, I do that sometimes) that I should be generous with praise for their good choices and obedience, as a way to encourage them to continue doing such. In a way, raising kids is similar to training a dog-- you give a command, they respond well, you tell them they did a great job and the next time the command is given, they'll remember the outpouring of approval from you and they'll want that again, so they will respond well again. Hopefully, right? I've never had a dog, I'm just going on what I've seen on TV and read...
Sincere praise, offered when you approve of your child's choices is a powerful reinforcing tool. I read some good parenting books and articles when my kids were tiny, and one thing I read that stuck with me was that instead of saying, "You're a good boy", (which is rather vague and comments on their personal worth rather than their actions) you should say, "Great job! I love the way you organized your closet, thanks for helping out!" or something. It's more specific, compliments the child on their behavior, and reinforces that behavior.
I actually don't think there's anything wrong with telling my kids "you a such a great person", but that maybe it shouldn't be used in reaction to a choice or behavior. My theory is that if mom tells son that he's a "good boy" when he does something she likes, that means that when he makes a choice mom doesn't agree with or approve of (which is inevitable), son will think that makes him a "bad boy". I don't ever want any of my children to think they are "bad". They aren't. Their personal worth is not determined by the choices they make. And they will make choices I don't agree with. They will earn my disappointment sometimes, but I never, ever want them to think I think they are bad. Children of God are inherently good, and repentance is a major factor of our religion. Joyful, peaceful, loving forgiveness from our Heavenly Father is a huge part of being a Mormon-- I don't want them to decide they are unworthy of His love or forgiveness because they are "bad".
So, if you're not already doing it, praise those kids. You probably are, but if not, I hope you start. It's an investment in your relationship, their future behavior, and their self-esteem.
Contrariwise, when you disapprove, make sure your kids understand it's the action you are unhappy with. Reprimand as needed, but follow up with love and make sure you find many things to praise them for during the rest of the day.
If you've never heard of the "emotional bank account", this is basically what it is: don't 'withdraw' more than you've 'deposited'. If you are constantly making negative comments and never put anything positive in that account, it can damage your child's self-esteem, as well as ruin your relationship. So be careful. And be positive and praise-ful!