the colours printed are limited by the output device - each printing device has an output profile - or profiles (there should be a profile for each paper type - some papers will have a smaller or larger gamut of colours depending on the surface and its coating).
For our own printers, the sRGB is the closest WORKING profile to normal photo paper in the Frontier. The Pearl paper we run through it has an extended gamut of colours available - particlary in the red and green/blue areas. We are bringing a 12 colour canon printer online - and with some of the art papers the gamut (or range f colours) will be greater than regular photo paper, but some won't have as deep blacks etc, as the paper is mat and not coated.
The shape of the gamut of a printing device is not always an exact match to a working space - you might find that it will perhaps print some colours that your space cannot show - and more importantly there will be colours that it cant print that your space has.
sRGB is often chosen as it is a space that is almost fully contaned in the printing space of any output - so it will print every colour you see - if you use a space that is larger, like ADOBE98 there will be colours you might be able to see, but the printer cant. However unless you've spent more than £1000 on your monitor you won't see all the space anyway. In ProPhoto space it contains colours you can't even see!
The aregument goes, if you cant see it, the monitor cant show it, and the printer cant print it why use it?
For most day-to-day printing the sRGB is the safest - as you can preview how it will look on most monitors and the print will be a close match.
If you use ADOBE98 you run a risk of working with colours that can't be resolved - but just like in the days of film, you learn to revisulize how it will probably look...
