According to globalPackagesFolder NuGet Documentation, it allows you to change the location of the default global packages folder instead of Users{username}.nuget\\packages.
The globalPackagesFolder is a global cache of NuGet packages. This is where NuGet downloads NuGet packages to as a machine cache. NuGet may clean out the cache when too many packages are stored here.
The repositoryPath is the packages directory a solution will use. It is usually a path relative to the solution. It can however be a global folder on your machine but typically it would not be the same as NuGet's global machine cache.