Re: Warning: The KMZ file is not tiled. 512x512 tiles are recommended.
The tiling is not absolutely required - in theory it can render faster on the phone but I'm not sure how much difference it really makes. I do tend to tile but only as the last step - and keep a copy of the untiled as the original. Once tiled it takes some major effort (or tools) to put the tiling back together. In addition, if you need to use the KMZ after to validate something on Google Earth, you cannot change the opacity easily as there are multiple images under the "file" directory in the KMZ. The size limit (under 1.5??) is also no longer an absolute (I believe it is for the older MapRun app). Having said that, anything larger is likely wasted on a phone and takes up server space for the MapRun team. Similar to the opacity issue, no simple way to adjust the actual file size once tiled so keep the untiled!!
Utilities has a tool to tile an untiled KMZ. Also, if you are not aware, the newer admin page Admin Page has a useful function to create the KMZ from an image by lining it up with points in GE side by side. Works well for images that have not ended up being skewed in anyway.