I see a lot of fields when filling the product data e.g. Alt. Text in Images, Product Tags, Product Meta Fields etc. in Shopify - Which ones according to you are most important?
For SEO - the more content, the better.
People add extra metafields with specific information about their products to make them even more attractive - e.g., what materials they use, where the products were made, whether they are eco-friendly, etc.
So, fill in as much info as possible and add some extra fields to differentiate your products from competitors and please the users.