This is a very common question when parents first start sleep training. They're amazed at how long their baby has slept for and start to wander if it's too long. My answer majority of the time is let your baby sleep! Most books you read will say to "never wake a sleeping baby" which is true almost all the time. There are a few times that it is very important to wake your baby. 1) Newborn stage - There can be weight concerns, jaundice, and other medical concerns. In these cases, which are very common in newborns, make sure you follow your doctor's orders and wake your baby. 2) Naps that are running into bedtime are not a good thing. Wake your baby if they are sleeping too close to their bedtime otherwise you will have a hard time getting your baby to sleep and it may cause frequent night wakings. 3) If your baby is getting too much sleep in the daytime is another reason to wake your baby. This again will lead to frequent night wakings especially in younger babies that need to eat fairly often during the day. They will only try to make up for it at nighttime.
When you have to wake your baby up make sure to do it as gentle as possible. Open your baby's bedroom door and start making slight noises and let soft light into the room. Let your baby wake up gradually rather then abruptly.
Otherwise let your baby sleep! Do not wake your baby for your own social convenience. It's only going to lead to a cranky baby and a miserable rest of the day for you and your baby. If they are sleeping they most likely need it. If you're worried take a peak and check on them :) No harm in that unless they wake up every time that you do. To learn more about what your little one's sleep requirements are, grab your copy of my "Mom's Schedule Cheat Sheet". You will learn whether your little one is getting too little or too much sleep. Click below to get your copy!