I guess any where that you want to reduce flow.
So no good for filling the bath, sink, washer, dishwasher or watering the plants as it will just take longer.
If you use a hose to wash the car it might help? But using a bucket would save more.
For hand washing in a sink you want an airraiter so the flow is less but the volume looks the same.
Oh & you do have to watch that your boiler is suitable for such a low flow. Some instantanious ones will cut out at low flows.