Categories, as product categories, should be used for static information.
A typical use case of product categories is the classification of products into different product areas:
Each product is assigned to exactly one element of a product category. For example each product with the number 065ee2c025 belongs to men in the product category Product Hierarchy 1, but not to women or another element of this product category. Product categories should be chosen in a way that the assignment of a product to a category (usually) does not change (i.e., a product that is assigned to the category jeans will not be assigned to shirts later). Therefore, this is static information.
A parameter, as the e-commerce parameter, should be used for dynamic information. For example, you could track different colors of a product using an e-commerce parameter:
In the example, there are three colors - black, blue and red. Depending on the color chosen by the user, the corresponding parameter value has to be passed to Webtrekk. To only show colors for a specific product, you should filter on this product or alternatively add the dimension "products". You also could add other metrics as in the analysis for product categories above.
In general, e-commerce-parameters must be used to measure custom website goals.
Further information on categories and parameters can be found in the training chapter Implementation 3 – Setup Options for the Tracking of Elements.