Well we know a lot about oxygen, that can do some really cool stuff. Carbon also, notably cool. For its structural properties Iron is super awesome, but it doesn't work for everything. Aluminum can help fill in those gaps though, and when neither of those work, titanium is the go-to element. I can't imagine where we'd be without sodium, its so important in so many chemical processes. Our entire tech industry relies heavily on silicon. Lasers wouldn't work without those noble gasses, neon, xenon, etc. Uranium has unlocked nuclear power for humanity, thorium promises a potentially safety and cleaner future for that power.

Elements do a lot of different things and we benefit from all of them differently. It's hard to know what a new element would do for us, but there's always the potential for it to be important. What would our society look like without silicon for instance? Without computers the world would be very different, and until we had them, could we have any idea what we were missing?