How much does Armour Class matter?

I’m a sorcerer and I’m currently wearing ‘The Graceful Cloth’ and it gives me and Armour Class of 18. However despite what the name suggest I don’t find it very graceful to look at.

So now to my question, if I wear a normal robe my Armour Class is only 17. Would that 1 Armour Class be hugely important?