There is very little difference between them. Guided meditation, visualization, imagery, all have their merits. Basically, it's purely amatter of preference. I personally use use all the methods on different occasions, both for myself and for my dear clients.

It is great for relaxation and putting you in the alpha state. Meditations put you in the alpha state as well.

They say we get hypnosis all the time while we watch a movie, tv, advertising, read an book and etc. Anything that we get so involved in that we forget everything else except what we are doing.

When we get interesting in something we tend to tuned out other things that are happening around us.

Visualization is great for the mind tends to see better in pictures forms. The sense of smell, hearing, and taste helps as well. The more vivid we make it the stronger the visiualization is and we can hold it for longer times.

There seems to be a consensus in the other answers here so far, and it fits my own experience. I see little difference between the techniques and I have used all three to clear away distractions and to become more centered and focused. Essentially, all three involve a wakeful state of relaxation with the eyes closed (a process that brings about a higher output of alpha waves from the brain's occipital lobe.) I have used them all at various times in my life and for various purposes: relaxation/reducing stress, enhancing creative thought processes, boosting the effectiveness of a particular discipline (such as fasting, or a diet regimen), and preparing my mind for more effective learning.