Performance hit of having many Result Set of a single row - sql-server

Question

I have a TSQL code that relies on a stored procedure to select a row.
When I'm implementing a more complex TSQL script that will select many rows based on a condition, instead of having one result set of x rows I'm ending up with x result sets containing one row.
My first question is: is it a concern or the performances are close to what I would get with one result set of x rows?
Second question: does anybody think that a temporary table where my stored procedure insert the result (instead of a select) should be faster?
Edit:
Basically this stored procedure select all the items of a given HierarchicalObject.
ALTER PROCEDURE [dbo].[MtdMdl_HierarchicalObject_Collection_Items]
#relatedid int
AS
BEGIN
SET NOCOUNT ON
declare #curkeyid int
declare cur CURSOR static read_only LOCAL
for select distinct [Id] from MtdMdl_Item where [Owner] = #relatedid
open cur
fetch next
from cur into #curkeyid
while ##FETCH_STATUS = 0
BEGIN
-- select the item row from its ID
exec MtdMdl_Item_ItemBase_Read #keyid = #curkeyid
fetch next
from cur into #curkeyid
END
close cur
deallocate cur
END
ALTER PROCEDURE [dbo].[MtdMdl_Item_ItemBase_Read]
#keyid int
AS
BEGIN
SET NOCOUNT ON
SELECT TOP(1) [Id], [TimeStamp], [Name], [Owner], [Value]
FROM [MtdMdl_Item]
WHERE ([Id]=#keyid)
ORDER BY TimeStamp Desc
END

Answer 1

For sure you should better place all single output rows into resulting temporary table before selecting final recordset. There is no reason currently in your code to return one recorset containing all separate rows from iteration over cursor with sp;
Your MtdMdl_Item_ItemBase_Read is relevant a bit because after turning it into function you can avoid sp+cursor and complete the task with one single query using inline function.
upd
According to your data structure I understand that your [Id] is not unique which is source of confusing.
There are many ways to do what you need but here is example of one query even avoiding CTE for temporary result:
DECLARE #relatedid int = 2
SELECT top(1) WITH ties
[Id], [TimeStamp], [Name], [Owner], [Value]
FROM MtdMdl_Item
WHERE [Owner]=#relatedid
ORDER BY row_number() over(partition BY [Id] ORDER BY [TimeStamp] DESC)
Consider this SQL Fiddle as demo.
upd2
Example with inline table function:
CREATE FUNCTION MtdMdl_Item_ItemBase_Read (#keyid int)
RETURNS TABLE
AS
RETURN
(
SELECT TOP(1) [Id], [TimeStamp], [Name], [Owner], [Value]
FROM [MtdMdl_Item]
WHERE ([Id]=#keyid)
ORDER BY TimeStamp Desc
)
GO
DECLARE #relatedid int = 2
SELECT DISTINCT A.[Id],B.* FROM MtdMdl_Item A
OUTER apply (SELECT * FROM MtdMdl_Item_ItemBase_Read(A.[Id])) B
WHERE A.[Owner] = #relatedid
SQL Fiddle 2

Answer 2

Your answer is in below link you should use GROUP BY instead of DISTINCT
SQL/mysql - Select distinct/UNIQUE but return all columns?
And in below line of your code enter list of columns you want in your result
declare cur CURSOR static read_only LOCAL
for select distinct [Id] from MtdMdl_Item where [Owner] = #relatedid
So your query will be
declare cur CURSOR static read_only LOCAL
for select rows,you,want,in,result from MtdMdl_Item where [Owner] = #relatedid Order By [column name you want to be distinct]