Oil paint is expensive. Cause of this I'm frequently hesitant to expend large amounts of it even though doing so can yield much more expressive paintings. Using more paint, or adding thickening agents to it, allows you to use the actual texture of the painting as another visual tool. It also gives the painting a much more physically substantial feeling when it actually has physical depth and isn't just a collection of anorexic miserly dribblings of pigment.
So sometimes this frustration with my standard operating procedure makes me just start smearing away with a palette knife direct on the canvas. Rare, but it does happen. Though in today's world even this approach is laughably conservative as far as "art" goes. But, though it doesn't push anyone else's boundaries, it nudges up against my own, and all things considered that's probably whats most important.