You can get the identified name and description of any item you examine, even if you don't meet the other skill requirements.
E.g.: The Fallout world is a big cesspool of ignorance unless you're part of the FotA, BoS, the Enclave, or a similar group. Though you can get the basic statistics and description of any item you pick up, more detailed and useful descriptions often appear for characters with right stats (Science for energy weapons, Medic for super stimpaks, etc.). This is especially helpful for builder characters who pick up random pieces of salvaged technology in the wasteland. To know what tech elements make up any given piece of equipment, characters need the right statistics. However, a character with Mental Catalogue has so much experience with and knowledge of trading that he or she always gets the detailed description of an item.
The perk description was posted by J.E. Sawyer on the Interplay forum in 2003.