You know what they say about first drafts. They're often the most fun to write as you're telling yourself the story. They feel so right at the time. They are, by law, always a bit rubbish because the wonderful story you weave in your head inevitably gets mangled and compromised by the awkwardness of converting your pure vision in to words.
As I'm approaching the end of my first draft on my WIP (that's writer shorthand for 'work in progress' for those not in the know), I'd say all of the above is true. Except that, as I've had the benefit of completing and redrafting a novel under the watchful eye of my agent, I'm now able to spot crap in my first draft a lot more easily. In most cases, I've jotted down thoughts in a separate document I've called, with breathtaking originality and mind-bending subtlety, 'Stuff to put in second draft'. But there was one plot hole so arrestingly noticeable that I simply had to do something about it. It couldn't wait. Yes, it would mess up what went before, but I knew I couldn't live with myself knowing that I'd spewed out this avalanche of sticky turds. The detrimental effect on my novel would be enormous, and I'd only end up spending long, long hours fixing it later. So I may as well spend those long, long hours on it now...
Now, because I'm doing this, it's no longer strictly a first draft. BUT as I haven't got to the end of writing out my first draft, it's not a second draft either. How can it be? So it's obvious what draft I'm on. Yep, I'm on draft 1.5. It's not like I'm changing a few words here and there: I'm radically altering a big plot point. But at the same time, I'm deliberately not changing some stuff (if I kept on going back and fixing every little thing as I thought of it I'd never finish the 'first draft') and, like I say, I haven't 'completed' the story yet on page. And thus, it's draft 1.5.
As I grow and develop as a writer, I'll presumably master the fine art of draft 1.75, or some such. But not just yet, dear, as I have a headache.