How important is word count? For a lot of book length publishers it means little or nothing, but they do have a page count in mind and that is very important to them. Many of them do indicate a word count (and do their own calculation on pages), and if they do, they are serious.
I had a couple of manuscripts that finished up between 50-60k. I did that because the publisher wanted the first two I published in that range. Then I found the publishers I was trying to pitch these to saying they were too small, they wanted closer to 90k. No problem, I set myself to adding some subplots, fleshing out characters, taking the count up. So they should have jumped on the revised version, right?
It apparently doesn't work that way. I had broken the rules. I had sent the wrong size manuscript, and I didn't get to skip to the head of the line with a revision, I had to start over, and in some cases they didn't want to see the revisions assuming I had just 'fluffed up the original,' right or wrong. Maybe I had, but they didn't even want to see.
So I pitched them to some other publishers fresh. Their web sites or market listings didn't give a word count, but guess what? They came back and said they were too big. I told them about the earlier version I had which was smaller before I took it up. Was still a hard sell because again I had broken the rules. However, after a great deal of effort they are at least looking at them. Apparently the 'fluffing concern' is not as great going down as going up.
Word count is even more significant in contests. If a contest lists up to 3,000 words they don't mean 3,001. Why? Because they don't want to give even a one word advantage to another entry.
It is generally that significant in short stories and articles. Editors have a certain size space to fill and they know exactly what they need to fill it. If they ask for 2,000 words and we submit 1500, it leaves them space to fill. If we send them 3,000 words they have to cut it and they either are unwilling to do that or even worse they might take out the wrong things and totally destroy the story (as we see it). Most of the time they will do neither and just kiss it off.
The mark of a professional is to stay inside the guidelines whatever they may be. Sure we can be arrogant and say "I know they want 60,000 words, but this is absolutely perfect at 90,000, and I'm going to make them take it. Occasionally this will happen, but as a rule editors and publishers do not react well to people trying to run roughshod over them. If a writer accumulates significant following and gets into a strong bargaining position, maybe, but otherwise - - - -
I got on a kick of writing VERY short fiction a while back thanks to a writing program I attended. I'm talking 55 and 100 word flash fiction, and some thousand word shorts. I even sold a few of them, but that was gravy. What I was after was learning to say things more succinctly, and the short stuff really puts you through your paces on that.
So what's the bottom line? If there is a word count or page count, I'd say we need to take it as an absolute. It's there for a reason.