The ecommerce overview insight provides an overview of the gross revenue generated by your business in the given time period. This is represented as a trending line graph. In addition to the gross revenue, this insight also provides an overview of your overall financial health of your business by providing other metrics like total number of transactions, average revenue per transaction and conversion rate for the given time period.
If you find big spikes in revenue, look at what caused that spike: maybe it was a marketing newsletter announcing a new product to your regular customers, or a social media post to your Facebook fans. Knowing which sources lead to more conversion and sales will help you focus your efforts on them for higher returns.