I never worked at a company without there was some kind of database server available. Databases are needed everywhere in the daily business. There are a variety of usages in SQL databases.
For most ASP.net webapplication SQL server is used as a backend. For storing the entered data. Most of the time the database consist just of a few tables and stored procedure. Because of the low amount of concurrent users, low amount of data transported the performance mostly isn't a problem.
Database used in a ERP application on the other hand consist mostly of a huge amount of tables, stored procedures and functions. These database are used by a nice amount of concurrent users wich are most of time demanding more of the database by creating reports, olap cubes etc. Performance is an mostly an issue.
Databases are heavily used in data warehouse applications. A data warehouse application reads all data of a production database, transform it's to a multi-dimensional model and copies it a data warehouse database. In the ETL process performance is an issue