To me personally, there's nothing wrong with stacking sterling, especially if you can get it for $2 under spot. That being said, sterling is usually not in the form of bullion, but rather in manufactured products, such as jewelry, teapots, spoons, forks, etc. The reason for this is because pure silver is too soft for everyday use and scratches easily, so copper (usually) is added to make it stronger. Sterling is really only used here in the States and in the British Isles, though it's becoming more common elsewhere, too. Nowadays, sterling is mostly made into jewelry; silver teapots, asparagus servers, oyster forks, etc., are a thing of the past. So if you're stacking sterling silver, you're likely stacking antiques, or at least pre-WWII. There's nothing wrong with that, if you're into collecting antiques, but they can have a premium attached, unless you're just looking for scrap sterling. To me personally, every piece of antique silver is unique and precious in its own way, and would never scrap any of that, if only to save the history.
Sorry for being long-winded, but long story short, there's nothing wrong with stacking sterling, but I would recommend learning a little more about the history of sterling (or other grades of) silver. One potential pitfall, however, is that if the world were to end tomorrow, it would be hard to barter with sterling silver, as most people would hesitate trading a pack of sugar or a piece of bacon for a salt shaker, for instance, but they would probably trade it for junk silver, like 90% dimes and quarters. So there are some tradeoffs here.
For me personally, I love antique silver for the history, sterling or otherwise. But as you can see, I'm a little biased
