Pipelined functions, a very classic example is where you do a SELECT * FROM table name in SQL*Plus. What happens is, Oracle streams the data from the table..
Like watching a video in youtube.
Please note the word, 'Streaming'.. And in our function we define how many rows we stream.. Every streamed row is immediately available to the caller. Pipelining means in lay man terms, dont make me wait till you complete, give me what ever you have, and keep processing and updating me simultaneously.
In your last procedure, after piping every row, you initiate a sleep call for 10s , so the record is Streamed to the caller every 10s.
And, a normal table function will keep waiting until all processing work is done, and then it will return the reference to the result set cursor.
pipelined functions , they claim to save memory, is by flushing the content immediately, and hence the buffer being used is always minimal, whereas the round trips count get higher.