Yep, it is a very useful function.

Also, that tub water is really good for using for other things since it is already at room temperature or above.

If you like to boil water on the stove to fight dryness, you can use the tub water and save energy because it is already nearer to boiling than tap water and you save the use of more tap water and associated energy use. When it starts to get condensed, just let it cool and dump it outside to help the soil.

You can water you house plants with it.

Take some and put it in a basin or one side of a sink and use it as a prerinse or presoak for dirty dishes, even if you use a dishwasher it will save a lot of energy.

Any tub water you can carry outside and pour onto plants and trees will help keep the roots warmer and give them a little more time to resist the onset of winter while allowing the water to soak into the ground and help rebuild your local water table.