The best of Travis CI is it's user-friendly GitHub integration. If you are using popular programming language - you will not get any problems. Moreover Travis CI provides huge capabilities for further customization. You can use default patterns to configure your build, tests and deployment or write it by your hands, because Travis CI provides Linux shell where you can do anything you want. Travis CI docs are also user frienly and easy to understand.
Good integration with some services like Coveralls, Docker Hub.
You can use Travis CI only for Linux and Mac builds. If you need only windows - Travis CI is not your choise.
If you are needed to use sudo - your build will start on low priority outdated infrastructure. That means longer build time and longer queues.
Advanced configuration requires good knoledge in linux command line instruments, because there is no graphic interface for it.
I recomend to try it by yourself. Just open docs, find your programming language and enjoy!
I am using Travis CI to test my libraries, upload coverage to coveralls and deploy documentation to GitHub Pages. The main benifits are from GitHub integration. With Travis CI you no longer need to check build state for the different platfors of the pull requests by yourself, Travis will do it for you. After merge Travis CI will deploy documentation, binaries, make a tag, publish, or anything you want it to do automatically.