I use Zoom in my solo marketing practice to work with clients remotely, which saves a ton of time for both of us — rather than meeting in person. It's a great way to demo software, explain Google Analytics results, walk through a design, etc. I also plan to use it to run webinars for promotional purposes.
As I said, it's perfect for working one-on-one with clients to demo software, go over a plan, share a screen remotely to do just about anything. That saves so much time. And you can do all that with the free version. I'm looking forward to trying it out for webinars. I've sat through a few of Zoom's webinars that explain how to set it up, and they've been very helpful.
It's worked well for me for what I need so far, so not sure where it may be less appropriate.