Structured data refers to kinds of data with a high level of organization, such as information in a relational database. When information is highly structured and predictable, search engines can more easily organize and display it in creative ways.
The purpose of storing an index is to optimize speed and performance in finding relevant documents for a search query. Without an index, the search engine would scan every document in the corpus, which would require considerable time and computing power.
A major challenge in the design of search engines is the management of serial computing processes.
Thus having structured data is useful for the achieving better positioning in searches.