Depends on the board. Many use the rule of thumb, "If it ain't broke don't fix it," with regard to the BIOS, but I like to keep mine up to date.
The BIOS (from your perspective) will function basically like the settings screen for your motherboard. Updating the BIOS can improve and enable and refine a lot. But there's always the chance that it can mess something up too, as in the back end the BIOS is not only the page of settings but it dictates the entire way the motherboard runs.