Too much salt will inhibit the yeast cells and reduce the rise of the dough. High salt levels will also lead to the risk of osmotic imbalance if eaten in excess. This can cause hyperactivity and increase in blood pressure. Over the long term, this may cause heart and circulatory problems.
In my opinion, most breads do not need salt.
Sugar - is used to speed up the yeast activity within the dough. Sugars are metabolised more quickly than grain starch, so the yeast will work faster when sugar is added at the start. The sugar is used up and will not alter the taste of the finished loaf.
I will normally add about 3ml of sugar to a 1kg mix.