Trying to answer: why oak.
Oak imparts tannin and flavors to the wine.
just like they used to store and transport wine
in oak barrels in the past. It gives some wines
a bit extra.
Do not oak whites or blush wines. It does not suit most
of them well.
You can also oak a wine with chips when the wine has finished.
Then when it is aging add some oak chips and do continuing
tasting experiments.
When you have the desired oak level, rack the wine from the chips.
Last thing you can do is make an oak concentrate
by adding chips to pure wodka.
I described on my web-log last yeasr:
http://wijnmaker.blogspot.com/2007/11/eiken-extract-oak-extract.html
You can add this extract to a finished wine to test
if oaking suits it. Then when you like it you can add
chips to the aging wine.
Luc