Sometimes there are exceptions to the wait-till-you're-finished rule. An agent asked me to query; I did, with an explanation that the novel wasn't finished yet and perhaps I should contact her again when it was. She asked for a partial and a synopsis (which I'm now scrambling to write) immediately. But the thing is, she knew up front it wasn't done; in fact, I told her I didn't know the word count either. She still wanted to see it. Wouldn't recommend this as standard procedure, however.
There are lots of rules I yap about here, and almost all of them have exceptions. Some of you may have noticed I edited your emails to take OUT the weird and unusual things you did before I post comments on the blog. I do this for a reason.
By its very nature this blog has to give general answers. First, it's written from my experience base and no matter how hard hell freezes over, I'm not going to become Binky Urban and have her experiences.
Second, I can't parse out every possible exception because I'm missing very critical information : what you're writing. I don't mean just category (although I often don't even know if it's fiction or non fiction) but also the quality of the work you do.
Third, quality itself is subjective. I sold a book today that 26 editors didn't buy. It's the same book for each editor and I know darn good and well some of them thought I was nuts for loving it. (ha on them!).
My answers here are the default setting. Expressed another way: they are the hump in the bell curve and cover about 60-80% of the situations you'll encounter.
That other 20-40% will be the exceptions. But it's like keyboard shortcuts: you gotta know what you're doing before you starting reconfiguring your system or you're gonna end up with a hard drive crash and the blue screen of death..never a happy place to be.