Sharing the URL straight from the deck editor will mean when other people view the deck, it will be in their deck editor. There are controls in place so it doesn't overwrite any existing cards in the deck editor, but it still causes some user experience issues (e.g. the save button below doesn't work with the shared deck - it will save whatever deck was already in the deck editor). Using the Share deck button, and sharing that URL is the best way to share a deck.