i've also wondering how/why you feed a sleeping baby?
My pedi said that when babies start being able to go longer between feeds they will usually skip the 10 or 11pm feeding and wake up between 1 and 2, so "dream feeding" involves feeding them without really waking them up before you go to bed so that they don't wake up until later. It would make sense on a night like tonight where M ate at 6pm because I know he won't make it all the way till 6am, and if I can feed him now and then go to sleep myself I might be able to get a longer stretch. But I'm just afraid to try it lol.
I dreamfeed every night! The only times I did not, she woke up about 2 am. She never wakes up (just stirs a bit) when I feed her. I will probably do it until about 7 months or so when she is eating more solids. If you do it, just keep the lights off and aim for 10 or 11 pm. (that is the time the baby whisperer recommends)
For those wondering why you would feed a sleeping baby, it is so you can pick the time they eat and not them (i.e. 11pm and NOT 3 am). If your baby is a lucky baby who would sleep through the night without eating, then of course a dreamfeed isn't needed!