"That cake is too bitter!"
Translation:그 케이크는 너무 써요!
Yes indeed. As an adjective, it means bitter yet as a verb basically means to use. (i.e. time, money, energy, resource)
돈을 쓰다 = to spend money (literally to use money)
하찮은 일에 시간을 쓰다 = to spend one's time on the trivial matter/business
하찮은 = trivial = 사소한
일 = matter, thing, business, work