Jailbreaking can get you a lot of features you wouldn't have otherwise. It would allow you to multitask, which isn't supported on your model in iOS 4, along with a lot of other cool little tweaks. There aren't many drawbacks; some have reported decreased battery life because of it, but I haven't had that problem, and these tweaks don't always have the level of polish you'll see in something made by Apple, so you'll see the occasional glitch, but nothing too major.