You may have stumbled across the term 'circadian rhythm' before.
It keeps you energised in the morning and drowsy in the evening, prompting sleep.
It's essentially a 24 hour-internal clock controlled by a part of your hypothalamus in your brain, called the suprachiasmatic nucleus.
It loves routine.
If you go to bed and wake up at the same time every night, your body will become accustomed to that behaviour.
Your sleep cycle is also regulated by certain proteins, the levels of which rise and fall throughout the day, affecting blood pressure and heart rate.
They'll also affect your attention and cognitive ability - you'll get sleepier.
If you follow a routine, your body learns to increase the levels of these proteins (PER) in time for your alarm.
They'll start increasing an hour before you usually wake up, in anticipation of your rising. Hence you sometimes wake before your alarm, if you're an organised sleeper.
If you sleep through your alarm...
...it conversely means you probably aren't getting enough sleep.
Or that you aren't sleeping on a regular enough schedule.
Waking up at different times can throw off your internal rhythm - maybe (don't shoot the messenger) wake up the same time at weekends as you do on weekdays?
You'll feel more consistent and well-rested.
You've just got to weigh up how much those nights out matter to you.