Some years ago the Inland Revenue created a vast amount of unnecessary work for itself by starting to tax Catholic priests on their "income". Most of us have very little by way of income (usually just the stipends for the Masses we celebrate) and given our service to people/society status, it seems a little unnecesary to tax us on the little we receive.
Why does this idea matter?
It's important to us priests because we have little enough income as it is without then being taxed. Also, to be honest, we may have moral objections to some of the purposes to which our taxes are applied.