Is there evidence to prove allowing your baby to cry is a good sleep solution and NOT harmful?

I let my kids fuss for a bit before they sleep and they are happy children. my daughter normally will fuss for a minute and then talk to herself for at least 20 minutes before she hits the on on her glow worm and crashes and she's 15 months. If she screams for 5 minutes I go in to check on her, but I don;t feel the need to keep them up just because they whimper a bit at bed time. There is a big difference between letting them scream bloody murder and letting them whine a bit. Follow the guidelines. Let them fuss for 5 minutes and then go in. Parents should know what cry's mean what. You guys are acting like we leave the kids in there crying for hours at a time and that's not the case. We aren't lazy. Our parenting skills just differ. Notice she said a few minutes not hours. Get a grip people.