They say that the best insights are derived when you combine multiple different sources. The more unconventional the data source is, the higher the value.
Excel is arguably the most popular end-user application. Over the years, users have been entering important information in Excel files. Unfortunately, it is not easy to work with this data for many reasons.
OLTP systems have traditionally been the most important data sources for many years. They were followed by weblog analytics, social media mining, and, more recently, Industrial IoT.
Reference: Staging, Ingesting, and Transforming Excel files.