"Why use Wiktionary?"

I can answer that one. I have free access to the Oxford English Dictionary (OED), which is brilliant and generally more detailed and reliable than Wiktionary when it has the word I'm looking for, but their login page is so awful that I sometimes use en.wiktionary.org instead just to save my time and temper. Also, en.wiktionary.org has proper nouns, other languages, and occasionally it has some recent or technical English word that OED does not have. So if I'm doing some serious amateur research: OED. But if I'm doing a crossword and want to check that a word exists and is spelt how I think it is: Wiktionary.