Many skins have project templates for About, Contact, Site Map pages and so forth.
If the templates supplied with the skin are updated any already in use by a project should be updated too. If you switch to a different skin the template code maybe different, updating to the new skin's templates may be needed.
Normally this is a manual job, open the skin's template folder and then all of the templates in use in your project. Then you need to copy the content of those files and paste them into your project files. If you just replace the files themselves any information entered will be lost.
This tool simplifies the process, just select your project and run the tool. It will update all templates in your project to match those in the skin's.
Note if you have custom made templates you have two options. either keep copies of the templates, for each skin you use them with, somewhere and navigate to them when switching, or skip those templates and if necessary manually edit the templates as required for the new skin you are using.