sRGB, Adobe RGB, prophoto RGB. In the order have increasingly wider color gamut. to even see the color of the last one, you need to have a wide gamut monitor. for the later two to see, you also need programs which are color profile aware. once you convert from the latter two to sRGB , there will a slight loss of information in color, and possible subtle changes and shifts. it is not something that you get back but converting back. its like taking a raw file, converting to jpeg, and then converting back to a 16 bit tiff. you dont get more information by converting it to a format that has more information capacity.
most new browsers are actually color aware. I know firefox is, and I think IE 8 is. so if someone is using the correct web browser, they can see srgb and adobe rgb. of course, if their monitor is not properly calibrated who cares. If the program is not color aware, then all the colors will look wrong. it also depends on who your audience is. the improvements of aRGB are subtle so best case senario, your audience with a calibrated monitor and right program can see it.
Printing, most of the mass print places (costco, cvs, wall mart, and such) assume your image is in srgb and print in in srgb. some costco places actually allow you to use the printer ICC profile to see excatly how your image looks if you are using photoshop. If you are printing at home, with LR or photoshop, the most important thing is to have the correct printer/paper profile combination assigned, and you get most accurate representation of what you are seeing on your screen, as long as your screen is calibrated. Hope that helps. Others may come by who are better at explaining this.