Instead of deleting it, use it to infuse into something else. And in case you're thinking 'If something needs to be infused with something I was going to shard anyway neither one must be any good to begin with', then you're missing the point. That being you're constantly improving what you already have rather than simply throwing both away. It's like throwing dollar bills away because they're not twenty dollar bills, without thinking that by saving those dollar bills you'll eventually have a twenty dollar bill. ;) Remember also that even rare (blue) items may have a higher base level (the level without a +5 mod) than a legendary you have and therefore can be infused into the legendary to increase the legendary items light ('power') level. So don't think 'It's a rare. It's worthless' and immediately shard it. Save them for infusion of something you already have or may acquire later.