Why Would I use webpack over other build tools, and task runners?

Webpack is a bundling tool, not so much a task runner however it has a lot of extra tools that can be used with it to give it extended functionality and it can also do things such as code splitting. Grunt and Gulp are the two main competitors, with Gulp taking the lead, although NPM scripts are slowly being used more and more as a way to cut down on the amount of tools being used within a project.

I'd probably make it a point to learn more about each, and have a basic understanding of the differences between them. Depending on the project you are working on, and the team you are working with, you might use any of these tools. Currently I am working on a project that heavily uses both Browserify (a tool similar to webpack) and Gulp. I see Grunt getting used less and less, but that isn't to say it is obsolete, there are still plenty of developers who prefer it.

It would be a lie if I said I wasn't overwhelmed at times with the sheer number of tools, and technologies out there, but that is how this field is. The best thing you can do is learn about each tool, run through some examples to understand the differences, and know which tool to use and when.

Here are some excellent comparisons between these tools and give you a high level overview:

https://npmcompare.com/compare/browserify,grunt,gulp,webpack
https://medium.com/@preslavrachev/gulp-vs-grunt-why-one-why-the-other-f5d3b398edc4#.hp75xwp1m