When you boil water, it loses a lot of oxygen. Those tiny bits of oxygen make a difference.
If you’re making a good tea or coffee, you want that oxygen. It helps you taste the flavor. If you’ve already boiled water, you ought to dump it out, and start with something fresh. You can taste the difference.
However, one key to making great ice cubes is to boil water and let it cool, and use that to make the cubes. They are much stronger, last longer, and are prettier because they are clearer. Getting rid of that oxygen makes better ice.
Don’t just use water. Use the right kind of water.