The Reproject function can be used when creating a cache from a raster or mosaic dataset that is not in the required projection. For example, when creating a cached image service that may be integrated by applications with other cached services, it's important that they all be in the same projection. This is often a Web Mercator projection. Since the mosaic dataset cannot be reprojected, you can do one of two things—either create a referenced mosaic dataset from your mosaic dataset in the projection needed, or add the Reproject function to the mosaic dataset's function chain. Another example uses this function on the raster item in a mosaic dataset. When using the Cached Raster function, you may want to insert the Reproject function so the cache is created in the new projection. Raster items in a mosaic dataset can be cached when the processing is intense and you are trying to publish an image service that is fast, without caching the entire image service.