Soft proofing is the last process before finally printing your photos.
I never did that until I came across those out of gamut warnings in Photoshop, which resulted in odd effects on printing.
My research led me to soft proofing, which is available now in Lightroom 4 Develop module. Soft proofing allows us to see what is out of gamut in the particular printer profile. Treating the out of gamut areas or colours by changing the exposure, saturation or hue, we are left with what we are sure we will get printed, rather than leaving it to the printer software in what would be a hit and miss process.
http://tv.adobe.com/watch/whats-new-in-lightroom-4/soft-proofing-images/ is a link to Adobe site about this topic.