Some moderns choose to use the "k" to distinguish "real" magick from the sort of "magic" done by stage illusionists.
If I refer to the pioneering 60's television series Bewitched, for example, I'll likely say that they performed "magic"; even though it was depicted as real within the context of the show, it is still fantasy.
If I am speaking of the practices, for example, of the English occultist John Dee, I will write "magick" to distinguish his practices from twitching one's nose and turning one's mother-in-law into a toad.