Apple released the new operating system for Mac, called “Sierra” very recently. Users can update their Mac via Mac App store. El Capitan, the previous OS, is overwritten by installing Sierra.
The most impressive feature of Sierra is that Siri is available on Mac. Siri used to be a personal assistant of iOS machines. Initially, it was introduced to iPhone, and followed by iPad. But Mac had not equipped Siri so far. Cortana, the voice-guided assistant program in Windows PC was preceding to Mac.
Another function installed via Sierra is Optimized Storage. It works on Mac to save your local storage through uploading the data which are rarely used to the iCloud automatically. There are some other unique characters in Sierra.
I installed Sierra the other day. To be honest, I have not accustomed to Sierra, either El Capitan. It seems good to utilize Siri on Mac. On the other hand, how much Optimized Storage is helpful for you depends on your way of using iCloud. Basically, you can possess only 5 GB storage on the iCloud. It is not enough to store important files. If you have never utilized iCloud, Optimized Storage can profit you. However, I guess there is a risk that Sierra exploits data translation while you use tethering with your smartphone.
Some failures are reported around Sierra. It is common that a newly released OS contains several problems. The article below presents some typical errors on Sierra. Fortunately, I have not experienced these malfunctions so far. Actually, iCloud is slowly working, but it is unsure Sierra is responsible.
Techradar: macOS Sierra problems: Here's how to fix the most common issues
On the other hand, I have to say that Endnote X7, software for arranging academic articles, is not working on Sierra. The provider committed this issue, but it will not be fixed, perhaps. Then, I have to use Endnote X7 only on Windows PC.
Considering these facts, I recommend you not to install Sierra immediately unless you are an enthusiast.