These are used pretty often when doing data analysis. It's a simple way to group things together.
For example, find all users who have have been active at least 10 days. This provides a simple way to do a complex operation (if a user signs up Dec 29, a naive implementation won't catch that their 10 days is in January of the next year).
For example, find all users who have have been active at least 10 days. This provides a simple way to do a complex operation (if a user signs up Dec 29, a naive implementation won't catch that their 10 days is in January of the next year).