Topics in Conversations are a great way to organize and keep track of your Customer issues and discover if there are any patterns or recurring themes to get to the root cause of problems.
Collectively, Topic data can help you identify trends in your Contact Center.
For example, if an increasing number of Conversations are tagged with the Topic Defective for a particular product, you can use this data to present to your Product Team and possibly check a QA process. 
Use multiple Topics for a Conversation
Agents can associate multiple types of Topics to a Conversation. The more Topics applied to a Conversation, the more points of data you'll have to analyze.
See Add Topics to a Conversation for more information.
Topics report
The Topics report shows why your Customers contacted you based on the Topic(s) appliged, allowing you to detect trends in inquiries based on how often Topics are applied to Conversations. The Topics Dashboard is also a great place to get a general view of the frequency of Topics' usage across Conversations.