According to Catholicism, why is transubstantiation important?

Can somebody explain to me the Catholic view of Transubstantiation and why it is important? Because with my understanding of it, the priests pray over the bread and wine and it turns into the literal blood and body of Jesus, but still looks the same. I know that in Matthew 26:26-29 it says about Jesus saying that the bread and wine was his body and blood but I thought that that was meant in a metaphorical sense. If the bread and the wine does actually turn into the body and the blood of Jesus, what difference does that make compared to a protestant's communion other than the reverence you would give or any of the rituals done. As a Pentacostal we celebrate communion in my church; drinking grape juice and eating crackers in remembrance of What Jesus did for us. I'm not opposed to other views on the matter, I'm just curious.