About using group layer caches in ArcGlobe
Group layers in ArcGlobe can have their own cache. The group layer cache can be used instead of the child caches (rasterizing the group layer) or as well as the child caches (merging the child caches). In both cases, the group layer's cache will represent a consolidated view of the child layers.
Group layer caches can improve the performance of ArcGlobe by reducing the number of disk caches ArcGlobe has to render to the screen. Like all cache types, the performance benefits for a group layer cache become evident when areas are revisited.
Learn more about when to use a group layer cache
Rasterizing the group layer
Rasterizing a group layer consolidates the child layers into a single cache for the group layer, rendering all layers as a single image with a single cache. All the child layers within the rasterized group layer must also be rasterized. Any child layers that were not rasterized before will become rasterized when the option is enabled. In this way, the group layer will be drawn similarly to how it is drawn in ArcMap.
Rasterizing a group layer is particularly beneficial for group layers that operate as a single unit, such as background displays. By consolidating many layers into a single representative raster, the size of the cache stored to disk is reduced, and only a single layer is needed to be drawn, thereby improving performance.
The use of a single raster layer means child layers will share some layer properties. The symbol point unit size and the minimum cell size, in particular, can profoundly change the appearance of the child layers when the group is consolidated into a single raster. To avoid difficulties, set a common symbol point unit size and minimum cell size for all child layers before you create the group layer cache.
When you consolidate a group layer by rasterizing it, a single layer is added for the group layer in the List By Type 
view of the table of contents, however all the child layers are removed. The child layers are accessible via the group layer's expansion tree which only appears when switching the table of contents mode to List Including Group Layers by clicking the
button. While the visibility of child layers can be toggled in this list, it should be avoided as much as possible as each change in display for the group layer will result in the group layer cache being invalidated and generated again on demand. This can be very costly, as there are no child caches from which to develop.
Merging child caches
Merging child caches consolidates the display of each rasterized child layer into a single display cache for the group layer while allowing the child layers to keep and maintain their own cache. This improves the rendering speed by sending a single drawing layer to ArcGlobe.
Merging child caches is useful for group layers where you have one or more layers that you do not want rasterized. For example, you may have a group layer with elevation layers in it. The rasterized layers will render in an optimized manner, while non rasterized layers will render independently, as before.
Merging child caches can also be effective if you have a series of layers that display at different distance ranges, such as several display levels for a road layer. This option allows you to have individual caches for each display level and yet only send a single rendering layer to ArcGlobe.
When you consolidate a group layer by merging child caches, a new layer is added for the group layer in the default List By Type view of the table of contents, and the child layers are accessible via the expansion tree. While the visibility of child layers can still be toggled, it should be avoided as much as possible as each change in display for the group layer will result in the group layer cache being deleted and generated again on demand. This is less costly than for rasterized group layers, however, as the child caches are not affected by their visibility status, and it is only the final merged cache that will be invalidated.