You may have a series of repeating events that occur regularly, but with exceptions.
For example, a meeting that happens every Monday except on the first week of the month.
How would you set up recurring events for this pattern? If you create a weekly event on Mondays, you'll have to manually delete the event on the first Monday of each month which can get tedious.
Here's another way to do it:
Go to Year view to see how all the Monday meetings show up for the next 12 months.
You'll see that each 1st Monday does not have an event. On months with a 5th Monday, the meeting is there.
See also how to make weekend exceptions for repeating events.