Currently working on a fic for Fandom Giftbox (~800 words added today!), and I do exchanges all the time, besides some of my own fics, so I can say that when it's an exchange, I tend to be way more motivated to *get it done*. The longest thing I've written wasn't for an exchange (but I wrote it in three very intense weeks with an alpha reader I chatted with all the time about it), but the second longest thing was, and I know as it came to the last week of writing time I really pushed to get it done. Had it been for myself only, it would've taken a lot longer. Also, my WIPs collection is full of fics that I started and abandoned - and because there's no deadline to finishing them, there's a good chance that most will never be completed. So I'm sort of torn about deadlines, lol. I do like them for keeping me writing short stuff (1-3k pieces) for exchanges, so I don't get out of practice writing altogether.