I am migrating my library from Apple's Aperture to LR. I am not using the built-in tool in LR for this job. Question: should I include the XMP sidecar file for each photo? Would LR use/need this file to make my library transition easier? Other thoughts/experiences with major imports to LR? Thanks for the help.
The XMP sidecar files contain all edits, tagging, etc you have made in Aperture. Assuming you want to maintain the edits you have made in Aperture you will need to include the XMP files. (This also assumes that LR will read and correctly interpret the XMP.) Testing is certainly in order. I would think you would want to include XMP file, this would maintain your edits in Aperture but also allow you to create a virtual copy and "reset" edits in LR and start over with the original. (I believe this to be true but I have not used Aperture nor have tried to import from Aperture - disclaimer.)
The XMP instructions are for Aperture and probably will not be read by LR. I recommended to Ken to convert his files to DNG either using import option or Adobe's free DNG converter. LR will read DNG files and annoying XMP files are eliminated.