Спасибо, нашел в хелпе
http://webhelp.esri.com/arcgisserver/9.3.1/dotNet/index.htm#selecting_svcs_display.htm
По дефолту отключено
Dynamic Tiling applies to map resources that generate dynamic map images (not map resources associated with a cached service).
When Enabled, a resource-specific tiling scheme is constructed. The tiling scheme generates a grid with a cell size based on the current map control size. Each cell defines the bounds of a map image which will be generated if the map view overlaps its extent. As long as the map scale remains the same, the grid remains valid. As map image are retreived, they are maintained in browser memory and reused. When the scale changes the tiling scheme is reset and a new grid is defined. This option enhances end user interaction with a Web ADF Map control, but requires that the map service on which the resource is based is able to generate map images in a timely manner. It is possible that up to 3 dynamic map images will be request as the result of an extent change.
