Travelling between time zones is one way to mess up your biological clock and disrupt sleep. Jet lag can make you feel fatigued for days after being forced to adopt a new sleep schedule.
But your social life and work obligations can also pressure you into a sleep schedule that differs from your usual schedule, or from your body's natural cycle. This has been dubbed "social jet lag," and can have effects on cognition and health.
Here is an article from Nautilus that goes into some of the risks: Why You Should Fix Your Inconsistent Sleep Schedule.
Your sleep schedule has consequences for your cognition. That's why Cambridge Brain Sciences asks about when you sleep, in addition to how much you sleep when you fill out your lifestyle information. A consistent bed time is best for most people, when it's possible.