added more comments

src/Workspaces/Core/Portable/Execution/PinnedRemotableDataScope.cs

@@ -35,6 +35,9 @@ internal sealed class PinnedRemotableDataScope : IDisposable
 
         /// <summary>
         /// This indicates whether this scope is for primary branch or not (not forked solution)
+        /// 
+        /// Features like OOP will use this flag to see whether caching information related to this solution
+        /// can benefit other requests or not
         /// </summary>
         public bool ForPrimaryBranch => _storage.SolutionState.BranchId == Workspace.PrimaryBranchId;
 

src/Workspaces/Remote/ServiceHub/Shared/ServiceHubServiceBase.cs

@@ -34,6 +34,9 @@ internal abstract class ServiceHubServiceBase : IDisposable
 
         /// <summary>
         /// Mark whether the solution checksum it got is for primary branch or not
+        /// 
+        /// this flag will be passed down to solution controller to help
+        /// solution service's cache policy. for more detail, see <see cref="SolutionService"/>
         /// </summary>
         private bool _fromPrimaryBranch;