I've noticed a correlation between the way some would-be novelists feel about synopsis writing and the way some screenwriting bloggers talk about doing treatments: it's a pain. It stifles creativity. Having to write an active, present tense prose distillation of your narrative is akin to flossing or taking out the garbage. In short: it's a chore.
To which I say: bollocks.
Writing a plot synopsis or treatment is a development opportunity. It's a way to road test your story, to see if it makes sense and has enough juice to sustain the intended length. Your synopsis or treatment is a road map for your plot, but planning the journey doesn't stop you taking diversions or short cuts once you're writing.
A great treatment or synopsis should leave the reader itching to get their hands on the finished script, screenplay or novel. But too many writers devote too little time, effort and craft skills to this crucial document. Why? Maybe they think it's not real writing. Maybe they're so brilliant they don't need to bother with intermediate steps.
If you're writing a feature film or the pilot for a TV series, you're hoping it will get made. For that to happen, somebody has to commit hundreds of thousands, even millions to your project. Why should they invest all that cash if you're too lazy or stubborn to produce a synopsis or treatment? Swallow a little pride.
What about would-be novelists who fear writing a synopsis up front will kill their enthusiasm for the putative book? That's an attitude I only tend to find in people who haven't written anything to length. Those who've done the hard slog and completed the first draft of a novel are less likely to be sniffy about the value of pre-planning.
I know, I know, in Stephen King's tome On Writing he talks about the fact he doesn't pre-plan his novels. He prefers a total journey of discovery approach. I meet the occasional scribe who's read that book and assumed King's example gives them carte blanche to avoid ever writing a synopsis. It works for him, why not them?
But that ignores all the chapters in On Writing where King talks about the years and years of learning his craft by writing short stories and novellas. King has spent decades acquiring enough skill that he can set off on a novel without a synopsis as his guide. Good for him. But unless you're Stephen King, a little foresight goes a long way.
I should stress that all of the above is merely my opinion. Your mileage may vary. Onwards!