Utterly is an intensifying word: something utterly delicious is very, very delicious.
One thing people love to do is exaggerate. You often hear people talking about how awesome or awful things are. When you're laying it on thick, utterly is an utterly useful word: it means something similar to completely, totally, or very. Something utterly disappointing is extremely disappointing. Something utterly wonderful is wonderful times ten. When you get tired of writing very, utterly is a good word choice.