AngularJS utilize web front end technologies (HTML & CSS) and don't abstract them out with extra layer like what other frameworks; therefor you require a strong web front end framework to work with AngularJS providing standard language, will supported framework and a plug and play responsive implementation.
let's consider the other options that works with AngularJS:
- not using a framework and create everything from scratch: unless you are a very good web developer with a strong team supporting you and plenty of time; avoid this option, this requires long experience and knowledge in web technologies not to mention compatibility handling, responsive implementation.
- using other frameworks: i don't see many reasons not to go for other frameworks like ZURB Foundation other than personal taste and good support; bootstrap is wildly used now and well supported, and you can find plenty of snippets and template websites online such as Bootsnipp.
bottom-line using bootstrap with AngularJS would definitely increase your productivity and chances of success, reduce cost and implementation effort, personally i think the mix is priceless.