See below. Dialysis is initiated if your nephrologists determines you have inadequate kidney function, some cases are reversible and they can determine if you have recovered some function and hold dialysis.
Complex question. Assuming that you mean withdrawing dialysis permanently and allowing death. When the patient cannot benefit from the treatment. We prefer to not prolong life in the face of brain death, severe disability, untreatable cancer etc. Each case must be evaluated and decided individually. Decisions should be made with familys and pts who vary widely in acceptance of withdrawal.