I like to live a basically decluttered life, but as someone who is also thrifty and a little sentimental, my downfalls are always cheap books and gifts. I buy very little for myself besides food and the occasional replacement for something essential that has broken, but my shelves and drawers continue to fill in response to the generosity of others. So stuff encroaches, and the occasional purge is always in order.
As much as I want to do a total declutter before Baby arrives, I know that isn't actually going to happen ... but this book did give me some motivation to get rid of things as I can (which is not what Kondo recommends, btw.) I did read it before I did my annual book reorganizing, though, and I was able to purge more books than I've ever purged in an annual reorganizing before (although still not as many as she would have liked me to, I'm sure!). I have to translate her question of, "Does this bring me joy?" to "Do I want to drop everything and start reading this book RIGHT NOW?" when I organize my books, and because my reading appetite is so voracious and my tastes so varied, the answer to that question is "yes," for practically every book in my house. I use the "spark joy" criteria for the books I've already read, but that is a small portion of my collection since I tend to set books free after I have read them.
The question about whether a possession sparks joy or not is the most useful part of this book, the most publicized, and one that you honestly do not need to read the whole book to start applying. It also pretty much ignores practicality, and the many things that you keep even though they don't spark joy necessarily, like your cutting board, your dishwashing detergent, and your toothpaste. She also prioritizes space and simplicity above all else, and if that is not YOUR personal priority you are likely to butt heads with her philosophy. For example, she discourages "stocking up" on items such as toilet paper to cut down on clutter -- but if your priority is time (not having to shop as often) or cost-savings (it's cheaper to buy in bulk), then you have a right to act according to *that* priority rather than to hers. I for one am not going to stop buying non-expirables in bulk because I don't like to shop OR to know I'm spending more than I need to.
She also assumes a certain amount of privilege in assuring readers that they can "buy another one" if they find they've discarded something that they truly do need six months later. My husband points out that this is sound advice if your space is so small that you'd be paying for a bigger house or extra storage space just to keep something around that you only use once in a while, but if those are not issues and you can't afford to buy a new pet taxi every time you take your cat to the vet even though it's just once a year with the occasional emergency, well, just keep that pet taxi tucked away in the basement somewhere.
As the book goes on, the sensible and helpful advice on downsizing devolves into "my way is the only right way" tips on organizing that border on the neurotic. Socks must be folded a certain way, clothes must be hung in a certain order, etc. While I'm all for folding my clothes in a way that makes them easier to fit in my drawers and access easily (although I still have to learn her folding technique and actually try it), there's no way I'm going to empty my purse and repack it every day -- I have a hard enough time getting out the door on time as it is.
All-in-all, this is a good book to motivate you to start decluttering and downsizing, but take it with a grain of salt and don't let Kondo's insistence that her way is the only way stress you out.