Parameters are filtering options that you add to a report to prompt the user to specify which data to display on the report at the time of viewing. For example, you could set up a parameter that prompts the users to specify the accounting units that they want to see in their report.

Use of complex parameters cause delay because Reporting Services must re-filter the published data.

These are the types of parameters:

Report parameters
Report parameters are either simple or complex parameters that are embedded in the Crystal Report. When the report is published in Reporting Services, the parReporting Services parameters are published into the Reporting Services repository. When users run a report with parameters, the parameters page that you specified appears and prompts users for parameter values based on either a hard-coded list or the data that they have access to based on the values in the system's rights files. When the parameters are submitted, Reporting Services refreshes the report by accessing the report's data source and fetching only the data specified by the report parameters.
Report Parameters allow you to select the type of parameter page the system displays to the user. After you publish a Crystal report to the Reporting Services repository, Reporting Services uses the default Reporting Services parameter page. You can select to override this page with the standard Crystal parameters page. Finally, you can add custom parameters that you specify within the report's Event preferences. Custom parameters pages allow you to display the user with a look and functionality that is standard to your company. For example, your company's logo, colors, and standard terminology are displayed on the page.
See Custom report page.
User parameters
User parameters are parameters that are defined in the Reporting Services application for a specific published Crystal or Lawson Applications report. User parameters are simple prompts that do not contain complicated set ups using functions or ranges. For example, you can add a user parameter to a report asking a user to select a specific accounting unit or company.
User parameters filter the data on the existing report instance and, unlike reports with report parameters, the system does not refresh the report.
Event parameters
Event parameters are parameters that are passed by Reporting Services to a custom Java method that is included as a Reporting Services event. As a result, the parameters are processed outside of Reporting Services. These parameters are primarily used when you want to integrate your report with another application.
See Report event overview and Adding or modifying events.
Cascading parameters
Cascading parameters are a series of parameters that derive their values based on the previous parameter selections. When you add cascading parameters to a report, you create a parameter whose final value is determined through a sequence of choices. For example, you can add cascading parameters that prompt a user to select a country before the choices for the region are displayed. The user is then required to select a region before the choices for city are displayed.
Reporting Services does not support Crystal Report’s cascading parameters. If you want to use Crystal’s cascading parameters functionality, you must create the Crystal Report, add cascading parameters, publish the report into Reporting Services, and delete all report parameters from the Maintain Report Parameters screen. This process forces the report to use the default Crystal Report’s parameters page.