People either like nickeled cases or they don't. I personally like them for at least a couple of reasons: 1) they are easier to size than unplated cases; 2) it makes it easier to identify a particular load if one special load is used for a caliber and the other loads for that caliber are in plain brass.
I've been told by a former Speer employee that they were used because in the leather belt loops of cops they turned green. Can't have police running around looking sloppy.
I've some nickeled .44 mag cases which have been loaded about 20 times. I only use them in .44 mag, .38 Spl., and .357 mag pistol cases and all my pistol dies are carbide so scratching probably isn't a problem with those.
I read an article a few years back which said that .38 Spl. nickel cases split more easily than others (reason unknown) and that they usually did it early on. I have found that to be true. Once the nickel cases have "proved themselves" by being loaded a time or two without splitting, they seem to last well.
I have read that these are brass cases which are plated. I haven't bothered to check that by scraping off the plating or anything, but I assume it's so.