The fact that developers at Microsoft decided to use an open source JavaScript library to build their user interface, instead of creating their own, is very significant. If you are familiar with SharePoint 2013 search components, you learned how to use Display Templates. In essence, Display Templates is a relic from when Microsoft developers built solutions without third-party dependencies. Display Templates mix HTML and JavaScript and allow developers to customize the way search results look.
However, it is a SharePoint-only technology, which means that it is much more limited and not as well documented and supported than modern open source libraries. This decision was made for you, instead of you making your own decisions.
With Office UI Fabric, Microsoft offers an open source project for use. When using Office UI Fabric, you can stick with Fabric Core, which includes core elements, such as icons, colors, and the grid, or depending on your framework choice, you could utilize...