Another use of srand is to obtain the same value of rand in a determined time interval. Example: you have an array of 100 elements and you need to obtain a random item every day but not to change in the 24h period (just imagine "Today's Photo" or similar).
<?php
$seed = floor(time()/86400);
srand($seed);
$item = $examplearray[rand(0,99)];
?>
You obtain the same value every time you load the page all the 24h period.