Publisher's Weekly (PW) has many benefits and one significant drawback--the cost. A one-year subscription to the magazine in print is $239.99, and a one-year subscription to the virtual edition is $180.00. If your business is writing, you'll get special offers that will save you some money, but no matter how you look at it, this is not an inexpensive venture.
There is a lot of great material online for no cost, however I recommend the purchasing the virtual edition (who needs to recycle another magazine, plus you save nearly $60!) because PW has so many useful features that you'll be shocked you ever lived without it.
What's so great about it, and is there anyone who won't benefit from it?
I'll deal with the second part first. There are probably people for whom it is less necessary, but I wouldn't go so far as to say that they wouldn't benefit. People who are going to write what they're going to write and don't care about what's actually going on in the industry will find it less helpful. However, even if no one can persuade you to alter your focus, give up on your idea, or make it fiction rather than memoir, you can still benefit from PW, and here's why (i.e., here's the answer to the first part) . . .
If you're a writer, publishing is your industry and it behooves you to keep abreast of its ever-changing landscape. PW tells you who is coming and going, as well as what companies are merging or going out of business. It tells you what books are coming out and who the agents are (and that could be your cue to write an agent if your book is similar to one listed). It devotes entire issues to mysteries, romance, health, and many other topics and genres. It reviews books (that's where the coveted "starred review" can be seen) and has author interviews.
Because there's so much useful information online, here's what I suggest before purchasing any kind of subscription: Spend some time on the site, and also purchase a copy of the magazine. Determine which sections are helpful to you and which aren't and whether you can get everything you need online. If you're in the business of writing, you always need to weigh how much something will cost against its advantages and disadvantages. This particular purchase, similar to a subscription to the Oxford English Dictionary, is one that requires deliberation.