I wear prescription shades. Pretty much always wear them, until the seasons steer me toward just wearing my regular glasses. I wonder from time to time about contacts and regular shades, or contacts and those fancy biking glasses w/ swap-out lenses of a color for every time of day and latitude, or prescription glasses that tint according to external light, or clear glasses w/ better shape to protect my eyes for riding in the dark, but I muddle along w/ goofy bug-eye shaped sunglasses from costco by day, regular clear lenses (small, wire-frame) by night.

ps-> re necessity or nicety, our family doc included sunglasses w/ sunblock on something our kids should never be w/o. Maybe that's just 'cause people around here tend to way overdo it during our 3 sunny months/yr.