I asked the same thing just a couple of weeks ago. I found that the rolling technique is alot easier. I do it on 3 strings too because it just helps when doing 5 string sweeps with rolling. It's also easier to do excersises like this:

---------------12-17p12----------------------12-17p12-----12-17p12----12-17p12----------
------------14------------14-----------------14----------14-14----------14-14--------14--------
----------14----------------14-------------14--------------14--------------14------------14-------
--------14--------------------14---------14--------------------------------------------------14------
-12h16-----------------------16-12h16-----------------------------------------------------16-12~
------------------------------------------------------------------------------------------------------------