I have come across a fair amount of that coper colored steel wire, mostly used for COMM links, where a bit of extra resistance is not a big deal. BUT the stuff is mizerable to work with because it is quite stiff steel, difficult to bend for terminals and inside wiring. BUT it does not seem to stretch and sag. So THERE IS A PLACE FOR IT, just not everywhere.

Your right about its being stiff. I could tell before I measured it if it was going to be CCS. The strands also tend to break. There is a place for it - in the bin - but I think it was sold off for small 100V line audio installations.

 

RFEaly the copper covered steel works OK for phone lines where it needs to go a long way between supports. Then one time I replaced a light switch for an old person in an old house and came across the same CCS wire in a light circuit. Fortunately they paid with cash and I did not leave a receipt to relate me to the work. If there is ever a problem my name will not be on any records. CCS is not code for mains power anywhere.