Based on the scope at which they are applied, product attributes can be classified into three types:
Product-specific attributes, i.e., the attributes configured on the level of specific products, like attributes for the product “Women's Tailored Dot Shirt.”
Product class attributes, i.e., the attributes configured on the level of a specific product class or group of products, like attributes for the product class Apparel.
Global attributes, i.e., the attributes assigned to any or all the products in your store.
When you decide to set up some attributes for a product, you need to consider what product properties may be important to buyers and decide whether they are specific only to this particular product or some other products in your store. This will help you to decide which type of attribute you will need to configure.
For example, if you sell t-shirts, you may benefit from setting up such attributes as “Size” (S, M, L, XL), “Color” (black, white, red, etc.), “Fabric” (100% cotton; 57% Cotton, 43% Tencel®; rayon; etc.) and the like. In addition, if t-shirts are the only type of products you sell, you should consider setting up the aforementioned attributes as global; this way, you will be able to use them for any SKU in your store.
If, besides t-shirts, you sell other types of products (for example, bags), the attributes of Size, Color, and Fabric may not quite fit these other products. For example, size is an important characteristic of a bag. Still, your customers are sure to find it much more useful if you write out each bag's dimensions in inches or centimeters than use the clothing-style sizes S, M, L, and XL. Similarly to this, bags may be made of fabric and leather, suede, plastic, straw, and other materials that may not be called just “fabric,” but rather “material.” So, in this case, you should consider setting up a separate product class for each type of your products (for example, “Apparel” for t-shirts and “Bags” for bags) and go with separate sets of attributes for each of them (for example, Size, Color, and Fabric for the product class Apparel, and Bag type, Material, and Dimensions for Bags).
Then, if one of your products has a property not found in any other product in your store, you should add the respective attribute on the level of this specific product. For example, if you have a single t-shirt style with embroidery, whereas all the rest of the t-shirts you sell are not embroidered, you can specify what types of embroidery motives are available for this t-shirt by configuring a product-specific attribute just for this very t-shirt style; for example, Embroidery (Butterfly, Flower, etc.).