I'm new to this and would like to serve images in UTM NAD83 zone 12 (Alberta, Canada) to a variety of products including some that would consume them in geographic WGS84. Do I need to list anything in the transformations or is this done automatically on-the-fly?
As long as the raster data added is defined correctly or specified during the add rasters to mosaic dataset, then the mosaic dataset should project it correctly into the new coordinate system. If there is a specific transformation you would like to use, you can specify it under the default tab within the properties of the mosaic dataset.
I did define the projections and things have been working well so far.
I have been considering transformations to speed up my loading times, but I'd be the first to admit that I'm no expert. I see a difference in speed from the native projection of my photos (UTM NAD83) to WGS84 geographic in loading time, so I was wondering if defining the transformations would help me out. It would also help me to have more examples of typical transformation scenarios in the documentation.