When Crystal Reports has a date parameter it can include the date entered as part of the selection or you can choose to not have the date be included. This option controls if the user to asked to include the date or not. Some administrators will always want to include the date and not provide the users with the option. In this case you can turn off this option and the parameters page will not give the users an option, the date will then always be included.
Below show the parameters page with the option on and the option turned off.
The Include Date Parameter Option turned on.
The Include Date Parameter Option turned off. This will
include the dates entered.