Databases allow the storage of information that is used often by entire departments or whole companies. Because most systems usually depend on one or more databases, a failure in these databases can cause all of the underlying systems to go down as well. Imagine a business-critical database failure that went unnoticed over a weekend, making both the company's website as well as e-mail, unavailable. That would be a disaster! A series of scheduled reports that was supposed to be sent out would fail to be generated because of this.
This is why making sure that databases are working correctly and have enough resources to operate might be essential for many companies. Many enterprise-class databases also have table space capacity management that should also be monitored—even though a valid user may be able to log in, this does not necessarily mean that a database is up and running correctly.