Not necessarily. A platitude is a seemingly profound, but trite and unoriginal, even meaningless statement. They aren't necessarily useless. For example, to

Not necessarily. A platitude is a seemingly profound, but trite and unoriginal, even meaningless statement. They aren't necessarily useless. For example, to tell a bereaved widow that their significant other is "in a better place" is a platitude, but it serves its purpose. I do question whether platitude is the correct word, but "useless platitude" is only a pleonasm if "useful platitude" is a contradiction, which I don't believe to be the case.