What problem does this solve or what need does it fill?

It's just a syntax sugar for better entity code organization

What solution would you like?

#[derive(Bundle)]
pub struct PlayerBundle {
    player: Player,
    movement: Movement,
    transform: Transform,
    global_transform: GlobalTransform,
    
    #[child]
    sprite: SpriteSheetBundle,
}

What alternative(s) have you considered?

I can already spawn two entities and parent them together, but I would be easier to spawn an entity and alto spawn it's children.