Agreed however if you are using Lightroom for file management and processing of raw data and Photoshop / Photoshop Elements for further editing there is really no need to write to xmp.
After your editing and other file management options in Lightroom you use the edit in function in Lightroom to send the file to Photoshop (or another photo editing application) for further editing if needed. This function does not require you to write to xmp. Also no other non Adobe application can utilise the Develop Module edits from the xmp file.
To wit there is life without the use of xmp files and this is the main reason that I adopted Lightroom as the application for the processing of my raw files. Since I have been using Lightroom (2007) I have not used xmp files (other than to share with other users or the transfer data after I have returned from an external trip.). My workflow is "simple sweet" the metadata info is in the Lightroom Catalog and I do not have the need to manage xmp files.,
Correct and the only reason for having xmp write on is for recovery after a catalog corruption. Doing regular catalog backups is a good thing to do if you check the option for Lightroom to check the integrity of the catalog. There is only a need to keep the most recent catalog backup. If a catalog gets corrupted after a catalog backup the recovery process could look like this:
1) Copy the Lightroom catalog backup into the location where the catalog is normally stored for active use. In the same folder as where the previews are stored. This is now the active catalog.
2) For any new folders created in imported into Lightroom after the catalog backup need to be imported again into the active catalog (which is the one created in step 1 above). Lightroom will read all xmp files in the folder and copy the information into the active catalog.
3) For any folders where new files has been added, do a synchronize folder for each of them and import the files that were not in the catalog.
4) For any files that has been edited since the old catalog backup will have an ! mark in the thumbnail and you can click it and choose read from file.
Fortunately I never had to do this, but I do have xmp write turned on for that reason. Of course any virtual copies and collection updates are lost since the catalog backup was done. The performance impact on having xmp write on is very little.