For programs that need to loop through 2 or more internal tables in order to output data etc., the best option will be to first read the internal table for the given key. This will get the developer the index of the first record in the internal table that satisfies the given key. Using this index the statement: "loop at itab2 from index." can be used.
When just looping on the second internal table using the given key, the program has to read through all the records one by one until it reaches the record which satisfies the given key. Using the "Read" statement directly takes us to the first record with the current key and we can start processing from that point onwards. This will make a major impact where the internal table have in access of 100,000 records.