How and when to use SLEEP() correctly in MySQL?

Question

In relation to my other question today I am wondering how to use MySQL's SLEEP(duration) correctly.

From what I gathered reading MySQL Dev forums and very vague description in MySQL Docs I can't use it this way:

SELECT ...
SLEEP(1); /* wait for a second before another SELECT */
SELECT ...

So what is it good for then?

Answer 1

SELECT ...
SELECT SLEEP(5);
SELECT ...

But what are you using this for? Are you trying to circumvent/reinvent mutexes or transactions?