What does Skype for Business do well? Skype has the benefit of being one of the longest-running companies in the virtual meeting / conference space. Their network is reliable and the call quality on both audio and video are good. The integration with the rest of the Microsoft products is also an advantage.
What does Skype for Business not do well? Where Skype falls down in recent years is its lack of simplicity in software design. They've made attempts to piggyback on design trends to stay competitive with apps like Slack, but the result of those updates is an app that is ultimately more complex and harder to navigate than it used to be. That's probably why a lot of podcasters mention that they hold on to the old versions of Skype as long as they can, so they don't have to deal with the new interface and all its shortcomings.
What do you wish you had known about Skype for Business before using? Before diving into Skype for Business, I think it's worth thinking about what technology your company / team already uses, because there's a good chance the ability to make voice and video calls is already built in to the platform. Google's G Suite has it, same with Apple's iMessage / FaceTime, Slack, Facebook Messenger, WhatsApp, the list goes on and on. If you have any kind of modern messaging app these days, you can make audio and video calls on it, making Skype redundant.
Have you used a competitor to Skype for Business? If so, how does it compare? I've used many platforms for audio and video conferencing, including Slack, Zoom, and FaceTime. They all have slightly different feature sets and slightly different UIs but they all basically do as good or better than Skype does with the basic functions. As long as you have a solid internet connection, the platform you use for these is largely interchangeable at this point, unless you need something really specific like screen sharing or virtual whiteboards.