Partly style points, and partly practicality and beauty.

Spoke protector disks age poorly. Plastic gets discovered. The things crack. The look is cleaner without them, so I take the risk.

They used to be metal. Some of the older metal ones look nice, IMHO. Maybe someone should put out a line of spoke protectors in anodized colors.

Valve caps. Yes on Schrader. No on presta. They are redundant on presta and strip easily, so I don't bother.

Mainly I just run with what I feel looks good and is convenient. No big deal either way.