Print message comes out in batches

Question

I have simple query

WHILE ( @counter < 50 )
    BEGIN
        BEGIN TRANSACTION
        PRINT 'Counter = ' + CONVERT(VARCHAR(4), @counter);
        WITH    CTE
                  AS (
                       SELECT TOP 50000 * FROM MyTable
                     )
            DELETE FROM CTE OPTION ( MAXDOP 1 )
        SET @counter += 1
        COMMIT TRAN
    END

When I look at messages, the PRINT command does not return row every loop but shows up as multiple rows at ones. I have added one line and now it shows up 1 line at the time and the the whole process is much faster.

WHILE ( @counter < 50 )
    BEGIN
        WAITFOR DELAY '00:00:00.5' --< This line
        BEGIN TRANSACTION
        PRINT 'Counter = ' + CONVERT(VARCHAR(4), @counter);
        WITH    CTE
                  AS (
                       SELECT TOP 50000 * FROM MyTable
                     )
            DELETE FROM CTE OPTION ( MAXDOP 1 )
        SET @counter += 1
        COMMIT TRAN
    END

so why is it when I have added .5 second wait time to each loop iteration it actually runs faster and allows the print message to come out one at the time?