I had no particular aim, but I knew what I wanted and had my story planned, so I made the mistake of doing an outline of the book with chapters already titled instead of a WC goal, to keep my pacing and progression in check. I only realized 2/3 of the way through that it was severely constraining my writing. I tried to fit everything into these chapters the way I had planned it, and the story suffered as a result.
I had no idea exactly how long it would be, but I guessed after the first few chapters of my 2nd reworking that it would be around 120k. It ended up at nearly 140k, which was trimmed down to 134k after revisions and editing. It was only after I rejoined AW that I found out about the YA 100k taboo, something I'd never heard of (somehow missed, and I can't believe I missed it) in 6 years of studying the industry.
I think you should give yourself a goal, but don't let it hamper or block up your writing.
