NuGet Restore only restores files in the packages directory, but does not restore files inside your project or modify your project.
For example, if there has a package will add some reference dlls or add some content files into your project. After deleting these reference dlls and content files from your project, it will not be added when restoring this package. This will cause the your project could not find the missing pacakges when compile.
So we need use "Update-Package -reinstall" command to force reinstall the package references and content files into project.
Update the example for sharing projects in a team:
Following is my solution structure, the CommDLL project installed some NuGet packages and entire solution is managed by a source control.

I download this solution on another machine from source control use another user account and install another NuGet packages into the CommDLL project. Then use some content from the new installed package and build the project successful. Please make sure the package dlls has been added into your project and it has been set the correct HintPath in .csproj file.
<Reference Include="Newtonsoft.Json, Version=9.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed, processorArchitecture=MSIL">
<HintPath>..\packages\Newtonsoft.Json.9.0.1\lib\net45\Newtonsoft.Json.dll</HintPath>
<Private>True</Private>
</Reference>
Next, I check in this modified project into the source control. Please make sure you the .csproj file and packages.config file are checked in.
Now I get the latest version on another machine to get the modified content. After check out the latest version from source control, the package references are shown with a warning because the project is not compiled, which means the packages are not restored. Please rebuild this project, it will restore the packages for your project (make sure your Visual Studio 2015 has enable "Allow NuGet to download missing packages" and "Automatically check for missing packages during build in Visual Studio" before rebuild this project).
