Popa: I believe the Levush quotes the Rema’s reason as being that in his area it was illegal to cut hair on Sundays (those Blue Laws still exist in some states, actually) and thus he allowed them to be Makdim to Friday for Kavod Shabbos. If you are an a place where you can get a haircut on Sunday, I guess that’s a Tzad Lehachmir. Once again, though, it’s not that yuo need it. There’s no Chiyuv to shave. If you don’t want to shave, don’t shave. (Unless you actually look bad, which may be a lack of Kavod Shabbos and then this “Chumra” is obviously Meivi Lidei Kula anyway.)
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