You can specify whether a table view in the grid handles grouping on the client or on the server:
Server-side grouping: To enable grouping on the server, set the GroupLoadMode property of a table view to "Server". (this is the default behavior). When grouping is handled on the server, the grid performs a postback to the server every time a group is expanded.
<MasterTableView GroupLoadMode="Server" />
Client-side grouping: To enable grouping on the client, set the GroupLoadMode property of a table view to "Client" and the ClientSettings.AllowGroupExpandCollapse property to True. When grouping is handled on the client, groups are expanded client-side, without a postback. This means that the data for all groups, whether they are expanded or not, must be loaded on the client.
<MasterTableView GroupLoadMode="Client" />
<ClientSettings AllowGroupExpandCollapse="True" />
Note that with client load mode of the groups the GroupsDefaultExpanded="false" setting will work only for the root items. Once you expand a root group, its child groups will get expanded too.
For a live example that demonstrates the GroupLoadMode property, see Client group load.