When you have a babe at home, you're doing your best to find sleep whenever (and wherever) you can. That's probably why the idea of waking up your baby to feed them makes you want to laugh...and then cry.
So the real question is: Should you wake up your baby to feed them?
The answer will depend on your baby's age, weight and overall health. In general, the younger your baby, the more likely it is that you'll need to wake her up, and the older she gets, the less likely. There are a few things to keep in mind when you're asking yourself whether waking your babe is necessary.
Age and Weight
If you have a newborn (we're talking less than 2 months old), then you may need to wake him up to feed him, especially in the first weeks of his life. Newborns need a LOT of sleep and will fall asleep, even after they've been fussing for food. This is pretty much the most infuriating thing when you're nursing, and the girls are letting down. So, waking up your baby while they're semi-latched is a must. But, when you lay your baby down for a nap or for "bed", and they don't wake up every 2-3 hours, waking him up to offer the bottle or the nipple is a good idea. The goal for most pediatricians is to have babe back to birth weight by 2 weeks old, and the only way to make that happen is to keep pushing the milk.
Most doctors will agree that after 2 weeks (if babe is up to birthweight), it isn't necessary to wake up your baby to feed them. A lactation consultant that I saw with my first baby put it in pretty simple terms: if your baby needs to eat 10-12 times a day, then they need to eat more during the day to compensate for not eating as much (aka sleeping longer) at night.
Whether or not you'll need to wake up your baby to feed them will also depend a lot on your babe's weight. The more your babe weighs, the less likely that your doc is going to recommend waking up your baby to feed them. Keep in mind that a full tummy will usually result in a longer sleep time (am I the only one who can relate?), so try your best to time your feedings right before bedtime. If your babe isn't on a sleep schedule yet, and has been falling asleep before "bedtime", then you may want to wake them up to feed them before they're starving, so that you can keep them drowsy and sleepy and avoid a middle of the night wake-up call cry.
Reasons to Wake up Babe
So, let's say your babe is doing great on the growth curve for her age and weight, and is getting to that age where she's doing 4-6 hour stretches at night. This timing will be different for every babe, but most doctors will agree that sleep training earlier, rather than later, will be more beneficial for babe and mama, and will generally cut down on your transition time (aka the number of days when you're dealing with babe screaming at you in protest every time you're not holding them).
Some mamas like to do dream feeding when they're working on sleep training their babes. This isn't necessarily "waking" your baby up to feed them, but it is making sure that they aren't going through the crying, calming, and eating cycle, and then falling back asleep. Depending on when you put your babe to bed, you will time your dream feed before they would normally wake up, and cut back on the chances of babe waking up during the night.
If you're a nursing mama, you might want to wake up your babe to feed them anyway. If your milk is coming in, or you produce a ton extra, you may be getting uncomfortably full at night without nursing. Most mamas will find that their milk will regulate so they're not waking up in a puddle of milk when they don't breastfeed every few hours, but don't hesitate to put baby to the breast to relieve your pressure when you need it.
Also, if your babe is going through a growth spurt, is teething, or is sick, waking her up to feed her may be a good idea. Making sure that your babe is getting her nutrients and calories in, during times when her little body is having a hard time, will only help. For sick babes especially, they will probably want to sleep the majority of the time, so do your best to at least offer a bottle or the breast to get some milk in them.