Photoshop :: Should A Photograph Be Reduced In Steps Or All At Once?

I've heard that when making a photograph smaller in Photoshop the results are better if it's done in steps instead of all at once.

If this is true how much should it be reduced each time and should the change in pixels per inch be done before reducing the image

My camera saves at 300 ppi at 3872 pixels wide (sometimes they are cropped which makes them smaller) and for the web I need about 500 pixels wide at 72 ppi.