Why use Twitter Bootstrap?
What's not to like? Out of the box, you'll get:
- Cross-Platform Support
IE 7 to IPhone and everything else (sorry IE6)
- 12-Column Grid
A good grid system takes most of the pain out of laying out your site. Getting labels, inputs, and other pieces of your ui to layout consistently across different browsers at different resolutions can be one of the most painful parts of web development.
Save yourself the work of trying to figure this stuff out on your own. The twitter kids have it under control.
- Responsive design
One of my favorite parts. If you craft your css/html a certain way, as the size of your browser changes (you can see this just by resizing the browser on your desktop), the layout adapts to display the information in a consistent manner as the screen size drops.
Viewing on a tablet and want to hide a left nav bar? No problem. Viewing on a phone and want to hide the menu bar? Too easy.
- Baked In Best Practices
Basically, if you want to get anything out of Bootstrap, you'll have to adhere to their best practices. Following someone's best practices is better than just hacking away at your CSS.
- jQuery Plugins
Great interactive components, built on everyone's favorite JS framework, that look and interactive fantastically with the rest of Bootstrap.
- LESS Infrastructure
I am a proponent of LESS/SASS/Stylus etc. If you've never used one, they allow you to do all sort of great software developy things with your CSS. Like set variables in one place for all the colors and sizes used by your app. Or re-use common styles without copy and paste. Or display certain styles if certain conditions are met.