Tips & Techniques:Phase as a widening tool

You can get instruments to sound like they are coming from outside the stereo image by using phase relationship. Start with a single track, say guitar. Pan it hard left. Duplicate the track and pan it hard right, but flip the phase 180 degrees. Start with the volume on the duplicate at nothing, and slowly bring up the level on the duplicate/phase flipped track. You will hear the guitar on the left slowly move out wider than it was when panned hard left. This will happen up to a point after which it will start shifting back towards centre.
Be sure to check things in mono, as there will always be some sort of trade off, but used judiciously this can add some interesting textures. Just cutting in on guitars in the chorus, or even used on just one word of a vocal to make it come somewhere else can spice things up. As always handle with care.

[John Suitcase]

Delaying the phase inverted track can further add to the effect, just a few milliseconds goes a long way.

As to the fan noise elimination comment, I think it would work with some types of noise, but with something periodic, like a large fan or an oscillating fan, you'd have to mess around with alignment a lot.

[The Peschinator]

The way you do it is leave them panned down the center and bring up the inverted audio until it cancels the sound completely. THEN you can pan them hard right and hard left.
And to be technical it's not exactly a phase relationship, it's a polarity relationship. You're not flipping the phase 180 degrees, you are inverting the polarity.