Help me understand Depth of Field quality (GI vs AA)

[GraceKellyPerfect]

So Corona Helpdesk states: "The quality of depth of field is mainly dependent on anti-aliasing (AA samples). To focus computing power more on anti-aliasing than on GI-sampling, you can decrease "GI vs. AA balance" value to about 4-8.".

Is the difference in quality only in less noise or you really get better looking Depth of Field with GI vs AA value lower than default (16)?

In 2 comparison images provided by the same article it looks to me that lowering GI vs AA to something like 4 only gets rid of noise quicker while DOF effect looks pretty much the same?

EDIT: To rephrase, does default value gets rid of jagged edges on sharp object like with lots of passes and small noise level <2% ?