You learned that placing your chosen keyword phrases into your Tags and Title help to be found. But you also learned that Tag stuffing and Title stuffing does not do any good. Etsy also says not to use generic terms in your tags such as "Stocking Stuffer" because it might be misleading. HOWEVER it is 100% okay to optimize your description for keyword phrases that are not allowed in the Tags section.
You can say your item is perfect for a Christmas Stocking Stuffer in your description. The Etsy search will look for exact keyword phrases in your description, so if you ran out of tags this is the perfect place to put them in. Just make sure that your description sounds conversational. Use your keywords you are trying to optimize for close to the beginning of the description and put things like exact measurements after all of that. It is rare that someone searches for a pendant that is 7/8 inch long. They will more than like be looking for a silver pendant or a steampunk pendant.
I hope this helps to clear a few things up for you. If not please feel free to ask a question and I will be happy to clarify for you.