A chord diagram helps to represent relationships between different entities. These diagrams place radially, which shows relations by flows. The higher the width of flow, the importance of the relationship is higher between entities.
Why do you need it?
We can see the connections between the entities in an attractive and effective way of just sight. This diagram just has a disadvantage, if the relationships between entities become more. The chart becomes clustered.
What kind of data you can visualize with it?
Data with relationships is best suited for this diagram. If you have different countries with their import and export to other countries in your dataset, then this diagram could be an alternative. The flows in this diagram will show the import and export between the two countries.