I shower simply because that is part of my morning ablutions toprepare for work.
Its not necessary to shower in preparation for a shave. Splashing your beard with warm/hot water works too.
When I don't shower, I wash my face, apply a pre-shave such as Proraso, soak a wash rag with hot water and hold that on my face for 1-2 minutes.
I have a fairly coarse/tough beard and doing so seems to help soften my whiskers so the razor doesn't pull.
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