I don't think it will hurt to call it. About the only time I use it is if I have to load the entire result set into an array for manipulation anyway (usually some heavy calculations, etc) and, obviously, there isn't a need to have two copies of the data in memory.
More often, tho, a large result set is simple displayed and it's best to do that by looping thru the data, so only one record is duplicated in memory at a time and I don't want to dump the result set before I'm done. By the time I've looped thru the result set, it's usually just a matter of closing </table></body> so not really worth the time.
OTOH, it's probably a good idea to get into good habits....