Sword "hole"

When it's a "beautiful flower ornamenting the handle", it's a tubular rivet. The "petals" are a washer over which the end of the rivet is bent outwards.

Whether the hole is vacant or there's a tubular rivet, if the hole is large enough, it can be used for a tassel or lanyard.

Sometimes, a bamboo pin, like a Japanese mekugi is used. Small empty holes might just have lost the pin. Or the rivet was removed to allow the grip to be removed. The tang would (traditionally) have been peened at the pommel (or, modern style, there's a pommel nut), so the pin is just for added security, so it isn't a big deal if it comes out, or the rivet isn't replaced if removed.

I've never seen one with a fake "flower". Maybe somebody does it. But a hole, rivet, pin or empty, doesn't mean a better constructed sword. The weakens the grip and tang (if the tang is wide and thick enough, it won't weaken it enough to matter). If it's empty, then the only possible benefit is for a lanyard. Some makers might (will!) use a pin/rivet to stop a grip with too much space between it and the tang from moving around. This disguises bad construction, rather than indicating good construction.