The first time you open this page will take some seconds to load the data from the service initially. All future accesses will be faster, because your DropDownList-Data is already stored on your local machine. To improve the user expierience use DDLCache_PreloadData() to load the DropDownList-Data in the background of your startup screen.

Use Fiddler or other developer tools to evaluate the difference of the network traffic size.

Check the source of this page, to see that only the selected DropDownList-Item will be transfered from and to the server.

Please compare the performance difference of both versions.

Please remember: This page does a normal PostBack to the server.