You don't ever have to justify your purchases. Well, unless you are married and the spouse is the one questioning it. I guess you might have to explain it to the IRS if you took a deduction for it, but that more of an explanation than a justification.
I remind you of the quote from Robert Heinlein (which I will paraphrase because I don't remember it exactly). He said that when a sentence begins with "It is none of my business but" that the appropriate punctuation is for you to supply the period after the but, using whatever force is necessary. I add to his that if the sentence should have started that way, it is the same.