In example below, every query with 'store' do steps:

1. Create temp table
2. Insert data
3. Query data
4. Delete temp table

Why?

My opinion that steps (1,2,4) no need execute every time

And second question, what difference between using Store method and using Enumerable value direct in query (see second 'for' in example)

namespace Sample
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using Xtensive.Orm;
    using Xtensive.Orm.Configuration;

    class Program
    {
        static void Main(string[] args)
        {
            var dc = new DomainConfiguration("sqlserver://localhost/DO40-Tests");

            dc.Types.Register(typeof(TestEntity));

            dc.UpgradeMode = DomainUpgradeMode.Recreate;
            var sessionConfiguration = new SessionConfiguration(SessionOptions.AutoActivation | SessionOptions.ServerProfile);

            using (var domain = Domain.Build(dc))
            {
                using (var session = domain.OpenSession(sessionConfiguration))
                using (session.Activate())
                using (var t = session.OpenTransaction())
                {
                    new TestEntity { Name = "Test name" };

                    t.Complete();
                }

                using (var session = domain.OpenSession(sessionConfiguration))
                using (session.Activate())
                using (var t = session.OpenTransaction())
                {
                    var list = new List<string>();

                    for (var i = 0; i < 500; i++)
                    {
                        list.Add("test");
                    }

                    var store = Session.Current.Query.Store(list);

                    for (var c = 0; c < 5; c++)
                    {
                        Session.Current.Query.All<TestEntity>().Join(store, o => o.Name, i => i, (o, i) => o).Count();
                    }

                    for (var c = 0; c < 5; c++)
                    {
                        Session.Current.Query.All<TestEntity>().Count(e => list.Contains(e.Name));
                    }

                    t.Complete();
                }
            }
        }
    }

    [HierarchyRoot]
    public class TestEntity : Entity
    {
        [Key]
        [Field(Nullable = false)]
        public Guid Id { get; private set; }

        [Field(Length = 400)]
        public string Name { get; set; }
    }
}

Queries (every query execute 5 times)

with 'Store'

CREATE TABLE [dbo].[#Tmp_55326e4a-bf32-4d62-afab-dbb52b5fc946] ([c01umn] nvarchar(4000) COLLATE Cyrillic_General_CS_AS)
exec sp_executesql N'INSERT INTO [dbo].[#Tmp_55326e4a-bf32-4d62-afab-dbb52b5fc946] ([c01umn]) VALUES (@p1_0);
INSERT INTO [dbo].[#Tmp_55326e4a-bf32-4d62-afab-dbb52b5fc946] ([c01umn]) VALUES (@p2_0);
INSERT INTO [dbo].[#Tmp_55326e4a-bf32-4d62-afab-dbb52b5fc946] ([c01umn]) VALUES (@p3_0);

...

SELECT COUNT_BIG(*) AS [c01umn1] FROM [dbo].[TestEntity] [a] INNER JOIN [dbo].[#Tmp_55326e4a-bf32-4d62-afab-dbb52b5fc946] ON ([a].[Name] = [#Tmp_55326e4a-bf32-4d62-afab-dbb52b5fc946].[c01umn]);
DELETE FROM [dbo].[#Tmp_55326e4a-bf32-4d62-afab-dbb52b5fc946];

with list.Contains(e.Name)

CREATE TABLE [dbo].[#Tmp_377456e1-ecb0-48ef-aedb-efde8a271453] ([C0] nvarchar(4000) COLLATE Cyrillic_General_CS_AS)
exec sp_executesql N'INSERT INTO [dbo].[#Tmp_377456e1-ecb0-48ef-aedb-efde8a271453] ([C0]) VALUES (@p1_0);
INSERT INTO [dbo].[#Tmp_377456e1-ecb0-48ef-aedb-efde8a271453] ([C0]) VALUES (@p2_0);
INSERT INTO [dbo].[#Tmp_377456e1-ecb0-48ef-aedb-efde8a271453] ([C0]) VALUES (@p3_0);

...

SELECT COUNT_BIG(*) AS [c01umn1] FROM (SELECT [a].[Id], 100 AS [TypeId], [a].[Name] FROM [dbo].[TestEntity] [a]) [b] WHERE  EXISTS (SELECT [#Tmp_377456e1-ecb0-48ef-aedb-efde8a271453].[C0] FROM [dbo].[#Tmp_377456e1-ecb0-48ef-aedb-efde8a271453] WHERE ([b].[Name] = [#Tmp_377456e1-ecb0-48ef-aedb-efde8a271453].[C0]));
DELETE FROM [dbo].[#Tmp_377456e1-ecb0-48ef-aedb-efde8a271453];