[Koha] Reason to define Koha item type in 942

Good afternoon, I recall reading (in the Koha manual?) the explanation for why it is advantageous to define Koha item type in the bib 942 field. I believe it has to do with exporting records, or the scope of records that is included when doing some type of report? I'm trying to locate that information again, but can't find it for the life of me. Does this seem familiar to anyone? Thanks. Tasha Bales Enterprise Services http://isesi.web.boeing.com/