Measuring for a mitzvah - "מדידה של מצוה". Preferably should be done on "ערב שבת".
Eating Hard Food When It Might Make One's Gums Bleed, and Removing Meat Stuck in One's Teeth When Gums Might Bleed;
(Melting ice.) putting ice into drinks; breaking off pieces of ice;
Lowering the Strength of a Fan, Dimming the Lights, Lowering the Settings on a Heater or Refrigerator;