For your appliances: If you have a CPAP machine, a steam iron, or a car battery, use distilled. The lack of minerals prevents scaling and buildup. Your coffee maker, too, but only if you want to clean it less often.
For specific medical reasons: Some people need ultra-pure water for nasal rinses or for mixing baby formula if you’re worried about contaminants. Distilled is your safest bet here. Your baby deserves the VIP treatment.
For plants that hate minerals: Some carnivorous plants or orchids are divas. They prefer distilled water because regular water can burn their roots. Let them be dramatic; they’re plants.