tl;dr
You can change the focus on a particular depth of field AFTER taking the picture, as opposed to having to do it BEFORE taking the picture.
7:07 to 7:12 on this video (skip the rest, it’s all useless) demonstrates.
[youtube=NsdEwr3TYTo][/youtube]
…although I gotta admit, this is pretty cool:
https://pictures.lytro.com/lytro/collections/41/pictures/1032687
(Let it load, then click on it and move it around)
[MOD: embedded video]