When we use repeater control in asp.net

You use it when you have a list of things to display, and you want to display them in some format other than a simple grid.

Suppose you have a list of employees, with name, address, phone, email, and you want to display them in some format other than a grid.  The repeater lets you define a template.  For example, you might display: 

Name
Address
Email
Phone

or

Name    (Title)
Address
Phone   /   Email

The repeater lets you define a layout for each record and then bind a list of records to it.  You can add controls if you want.  For example, you could make the email editable by putting it in a text box.

The repeater can be very handy.