Why excessive salt is used in the preparation of pickles and excessive sugar in the preparation of jams & jellies?

Why excessive salt is used in the preparation of pickles and excessive sugar in the preparation of jams & jellies?

A high concentration of salt in pickles make the germs to loose water from their cells through a phenomenon called  exosmosis.  Exosmosis  occur here due to a  difference in concentration of pickle (more concentration) and germs (less concentration) . Due to loss of water from germ cells they get plasmolysed and die. Thus the pickle can be preserved for long duration because the germs cannot stay in the pickle. Similarly, in jams and jellies also, because of high concentration of sugar, water from the germs will be drawn out and will be killed.  So because of this they also can be preserved for long duration.