climbing ropes are probably a bit more expensive and also more valuable (if you're still on a mountain and need it to get down, i guess you don't want to cut it unless you absolutely have to!), whereas if i've tied someone up, when we finish i tend to untie things slowly and tenderly. and if there's an emergency (fire alarm goes off, etc), i'd prefer just to cut the ropes and buy some more than to potentially spend time struggling with knots and putting us both at risk.