Pros
The flexible schedule gives you plenty of time to create your own extracurricular projects. You can do your own research, network, take lots of classes, or even just travel. Depending on the host institution, grantees may find that they have little oversight. This is great if you're a self-starter (and presumably you are, if you've applied for and gotten the Fulbright) so this makes it an ideal opportunity to make strong community connections, engage your students in non-traditional educational activities (you really succeed more the more creativity you show), and take an interest in the local culture. You can do so much with this time. Take language classes. Travel. Build relationships and display your individuality as a cultural ambassador for America. The only way to truly fail at this experience is not to try at all. Any effort you put in (ideally, you should put in your best effort) will be rewarded.
Cons
As I learned from my own experience and from the experiences of other grantees in my host country, host institutions don't put a lot of emphasis on giving you responsibilities other than teaching a few classes. That means you can customize your schedule and create as many projects as you want, but only if students are amenable. Which they probably will not be. So you may be stuck with a prestigious grant that carries weight in the US but has virtually no impact in your host country. There is almost no name recognition for its value, at least in smaller cities (even the ones that host scholars). My host institution leader even told me (on the first day we met) that he/she would have preferred to have a different type of scholar (an English Language Fellow rather than a Teaching Assistant) but that they were happy to have me rather than have none.