Ok, sorry it took so long to answer back, I came back from work and was a bit obsessed in making the map work...
So a gamut is simple "more possible colors".
Now. I know that professional photographers like to use ADOBE RGB because of the "color gamut” but most monitors can't show those colors. So if you’re sticking to screen presentation use sRGB, it has a lower color gamut.
Oh man, I wouldn't... if it were me editing my images all I would really want to get is the best printer out there so that the color gamut of the images actually translates to print. All I really see it doing is helping you edit a "bracketed" image (an image that has been shot with three different exposures so that the sum of all three = good exposure) What I would do is save my money and get the better printer (and really good printing paper).
Some people love it others say it's "just one more thing to make me lazy" ...
The thing to remember is that the way PS works when editing photographs, is that it wants to be in a wet lab. It uses the same basic principle as a color darkroom. So the way I always look at it is the "carving" of light of the hole image. The red histogram is going to show you where red stands in the image, what light carved it out, where in your image the carving of that red light changed.
Looking at color film (as well as the way levels and curves are seen in Photoshop) work with the principle of adding and subtracting one type of light.. light of a particular color. So if you just imagine having a piece of color film:
What happens is that light carves out places where the colors (or mix of colors) can create an accurate reproduction of whatever it is your taking a picture of. Histograms are that carving. Letting you know how much of red is in the shadow, highlights, etc.
Never use the histogram to edit color! EVER!
Always use curves. If you feel the need to use histogram only use it when your setting up your highlights and your shadows, after that only use curves.
Hope this helps!