Understanding monitor/printer profiles?

Jeff Peterman wrote:

>You should never 'apply' profiles, only 'convert' from one profile to another,

OK, I'm a little confused about the difference between these two. I think I understand "Convert", but what exactly happens when I use "Apply?"

As for sticking to sRGB, I know that when I used soft-proofing in CS5 with the printer profile as the target and then enabled the option to indicate out of gamut colors, I saw several blotches appear on a couple of images.

In both cases, a little tweaking of the colors/saturation brought the colors back into the range of the profile without having any real impact on the image, which means that the images SHOULD look smoother with the adjustment in comparison to just viewing them in sRGB.