This page have configuration settings for standard fields on Product/Asset/Config item
There are a couple of settings needed for some of the standard fields available on a config item (In contrast to the custom fields you can configure in Product Settings - Custom fields).
Both Vendor and Manufacturer refers to data of the Company type. But here, you can limit what companies are available in the two product/config item fields. In the example above, you can only select Vendor from companies of the type "Special", while Manufacturers are limited to those of the company type "Bogus".
The selections are of the type checkbox dropdown, which means you can select multiple company types. If no types are checked, this is the same as "All" - i.e all companies will be shown in the Vendor/manufacturer combos on the Product/Asset/Config item.
This feature is useful to limit those fields to just the companies you set as an actual manufacturer or vendor.
Note: You configure the available company types in the account settings under Company Settings - Company types.