My friend Damien recently shared his thoughts on using wordcount to measure writing progress. It's a useful thing to think about, especially if you are just starting out as a writer, and aren't sure how to measure your progress by anything other than the number of words you have written that day. Obviously, wordcount is a way to measure progress, and an important one. If you are trying to write a novel, you had better know what the standard contract length is for the genre you're working in, because you don't have a salable novel until you've hit that point, and you don't have a salable novel if you are too far over it.
(When I first decided I was going to write a novel, I looked to the awards guidelines to see how long a novel was. 40K words or more is officially a novel for those purposes. I'm very glad I learned before I started writing that if I wanted to sell something, it needed 60K more words to be novel-shaped.)
I don't use wordcount as a measure of progress. The biggest reason why is that I handwrite. So while I have a general idea of how many words are on each notebook page, I don't know for sure until I move the words from notebook to computer. But another reason is that, for me, wordcount is a bad way to measure progress.
I've always had a difficult relationship to wordcount. I am naturally a very concise writer. Brevity being the soul of wit and all, my papers in high school and college always came in at the short end of the requirement. Even when I loved the topic, and thought I had a lot to say on it, I'd be on the 7 page end of the 7-10 page spread. I am in a profession where short fiction gets sold by the word, and so wordcount matters. The longest story I've sold so far is 1900 words. In fact, if you add up all the words in all four of the stories I've sold so far, the amount is still under the word limit to be considered one short story in any of the major genre awards (short story being a work of 7500 or fewer words). At some point, I would really like to sell a short story that would be long enough to use in a Clarion application portfolio (I'm still not sure how I managed to write two that were the year I applied.)
But along with my conciseness comes one of the biggest flaws I am aware of in my own writing - I leave too much in my head in first drafts. My polished drafts are never about trimming the excess, but about adding all of the things I didn't put on the page the first time, and so they are generally 20% longer than my draft zeros are. So I tend to measure my progress by "have I solved the current problem?" This means I tend to write short stories in one sitting, and longer projects by scene.
Which is all, I suppose, a rather long-winded (shockingly enough) way of saying, like anything else in writing, figure out a way of measuring your progress that works best for you. Do whatever helps you finish things on the schedule you want them finished by, whether that's counting words, or counting scenes, or not counting anything.
Write until you get to the end. Then stop.