They look like flowers. Too early for seeds. Many double cherries and the like are sterile anyway. They will rot away where they land, or you could rake them up if you don't like them that much.
The flowers look more like Acer flowers, might it be Acer Platanoides Crimson King?Hard to be sure though, so I might be 100% wrong.
very few trees are "rubbish waste of space",