It's all about surface area, using chips and shavings mean there's a large surface area to the volume in contact with your wine. I do a bit of wood work so when I want oak I just get out the plane and shave some off some old wine barrel staves I have. That said I use sticks of oak (long and thin so they fit in the bottle) toasted in the oven to flavour cheap vodka (gives it a bourbon like taste) . The sticks toast better as they don't burn as easily as shavings but I put multiple saw cuts in them, again to increase the surface area.