If you apply a category filter and filter your items based on your store categories. Only the times associated only with the selected categories will be exported to the given product feed.

By default, the items from all categories are exported.

If you uncheck the Export ALL categories button you can:

You can select specific categories from your store category list.

The All mapped categories option allows you to select automatically just store categories that are mapped to the marketplace categories in the Category Mapping tab

You can select all your store categories by clicking the Select all categories option.

You can unselect all your store categories by clicking the Remove all option.