It doesn't let you hot plug your eGPU into your computer (you have to restart for it to work) but for officially supported eGPUs you're now able to do that.
I've trained various models using a Titan XP and it's so awesome to be able to maintain the portability of your laptop and still get all of that power. A large benefit is also not having to move training data around between servers and other machines if you have it on an external drive or just on your laptop.
After you get everything up and running there isn't that much maintenance or anything you have to do regularly to keep it working. The speedup is incredible and it was definitely worth it for me personally, however it's not a walk in the park to get it set up initially.
There are beta NVIDIA drivers (http://www.nvidia.com/download/driverResults.aspx/131833/en-...) for macOS, but your mileage will vary.
The reason for that is Apple hasn't shipped a iMac/MacBook Pro with an NVIDIA card in years, which is especially annoying for DL work.