I confess. I've never used oil or foil on a baked potato in my life. I wash off surface dirt, put on rack of my toaster oven, set somewhere in the vicinity of 425 degrees and ignore for about an hour. If I don't want to eat it just yet, I'll turn the oven down to 300 and ignore it longer. I'm weird.
How you make your potato will likely depend upon how you prefer them. Wrapping in foil will produce a softer skin and sort of steams the potato rather than baking it; leaving the foil off will leave the outside crispy. Oil and foil together seems to me counterproductive, but what do I know?
Here's a page with slightly different thoughts on the subject of baking potatoes in the oven and one on the subject of nuking them in the microwave.