Quite a few threads on here about climbing wall lower offs and use of screw gates etc. But havent quite found the answer to this...
At a local wall where there is a snaplink and a screwgate together on double bolt/chain lower offs. A notice says to clip the snaplink if you are just lowering off from leading a route (which makes sense - sometimes a pain when only screwgate and its screwed down tight) and to use the screwgate if top roping.
But it then goes on to say 'NEVER' (capitalised and in red) clip both carabiners' as it 'can result in damage to the lower off'.
Anyone care to suggest a reason - uneven wear on carabiners maybe?. The stress on NEVER seems to imply its highly dangerous.
(Even more confusingly, a seperate notice says to clip both carabiners at the lower off).