The reason for this is that the production, distribution and updating of Internet databases is fairly inexpensive in comparison with traditional means of publication, distribution and storage. As such, Internet databases allow individuals and organisations to provide substantially more information (both free and fee-based) to the public than has been possible previously.
Equally, they expand the number of individuals and organisations who can access that information. As an electronic representation of data, they also make it possible to utilise the information in a variety of ways previously unavailable or available only at considerable expense.
Take, for example, the US Census Bureau (http://www.census.gov). The statistical tables published by the Census Bureau can be downloaded directly into word-processing programs, such as Adobe Acrobat (PDF) files, or into almost any other dataprocessing programs, including Excel spreadsheets and mathematical or statistical packages.
All of this allows students and researchers to access and use far more data than has previously been available. This kind of data can prove useful at every stage of the research or study process, whether you use it as a starting point for developing a topic, or as a means by which to advance or focus the argument, or as evidence to be deployed in trying to defend the arguments you have made.