Hi Ben,
The main purpose of color management is to assure a color-accurate workflow. Probably you might have already experienced that your printed photos looks completely different than on your screen. This is due to the different color rendering of your monitor and printer. By applying calibrated color profile(s) to your monitor and printer/output device, the color reproduction will be matched (as much as possible) resulted in WYSIWYG
So if you have a calibrated profile, it is recommended to apply it for PhotoPerfect as well. Even if you do not print out photos, applying a monitor profile can make your photos look consistent when viewing them on different or multiple screens.
The visual difference after applying a monitor profile depends on how good your monitor actually is. If you have a highend monitor, you might only see subtle changes, as probably your monitor has already been calibrated by the manufacturer and bundled with a good profiled. Otherwise the difference on a less than optimal monitor might be "eye opening"
Best regards
Hoang-Tran