If for some reason, your rear wheel is built up with a disc only rim that doesn't have a brake track, running a rear brake would be detrimental, but I'd imagine the chances of that are rather small.
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Bikes: 1996 Eddy Merckx Titanium EX, 1989/90 Colnago Super(issimo?) Piu(?), 1990 Concorde Aquila(hit by car while riding), others in build queue "when I get the time"