Lightning Component framework has a rich set of JavaScript APIs that you can use to build client-side logic. However, there are a lot of open source libraries and frameworks that provide rich functionalities but can take a considerable amount of effort to rewrite using Lightning Component framework's native JavaScript APIs. One example of such a situation is if you are looking to build charts with Salesforce data, then building all the CSS and client-side JavaScript from scratch can consume a lot of time. Instead, you can import libraries such as ChartJs (https://www.ChartJs.Org/), HighCharts (https://www.highcharts.com/), or D3 (https://github.com/d3/d3/wiki/Gallery) to meet charting requirements with minimal code and without having to engineer everything from scratch.
Another example is using libraries such as...
