Why does NuGet check out all csproj-files in TFS on update-package?

I have a solution with multiple projects, many of the projects have NuGet packages installed, some of them have the same packages installed. When I run update-package NuGet checks out every csproj-file 开发者_开发问答and occasioanlly it also adds some app.config file to some projects.

Did those projects actually get updated? If so then the csproj file will get updated. app/web.config gets added if a package adds it or if you need binding redirects for the packages to work together.