This has been discussed N times here and there. As you pointed out, you save bandwidth and, if it used wisely, will boost your loading performance. That is the good thing. However it is positive that when you use it you take into account that:
- There is an implied external server response time to your GET request.
- Client may eventually block the CDN provider.
- Ideally, CDN servers must be located near your main user base to get the quickest response possible.
- You have to be careful on how many requests per page you do.