My experience with metal dowels are with metal applications only. Dowels, or dowel pins, as they are usually called, help in locating machine parts that are sometimes diassembled, such as a punch and die set, or gearbox cover. The dowels, usually 2 or more, assist in assembling the parts in the same location, as before disassembly. The bolt holes for the bolts that hold a gear cover on are usually not a precise fit, but the dowel holes and dowel pins are a very precise fit, sometimes requiring a tap in with a hammer. Hope this helps.
Larry

Thanks for the explanation both of you. I understand better now they're used for repeated assembly/disassembly whereas wood dowels won't quite offer the same quality over and over. I've noticed that on lower-end 3-in-1 and 4-in-1 cribs the sides are fastened with hex-driven connecting bolts but located with metal pins and never wood. Since the cribs are meant to be configured differently over the baby's early years that makes sense to do.