Octave and pitch effects aren't designed to change the tone of your guitar, but the notes themselves, and are a great way to add greater depth to your playing with ease.
Octave effects can be used to create notes an octave below the guitar lead line. Jimi Hendrix was known to use octave regularly – give Purple Haze a listen – and more recently Jack White has been using it to great effect.
Like the octave pedal, pitch will enable you to create note harmonies above and/or below your original guitar line to change it into a different key. You can then use it to extract a whole world of crazy bends and squeals from your guitar.