You definitely want to remove heavy wet snow from flat roofs or roofs that don't facilitate it sliding off (such as a shingled roof, or one with too low an angle). Standing seam roofs solve the issue. I still remember how giddy my mother was when we had one installed when I was a kid - she HATED roof raking.

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The folks who retreat to AZ and other warmer climes for the winter are likely to fall into one of two camps: either they have a standing seam roof so the snow slides right off, or someone else takes care of it for them while they're gone (whether a paid third party or groundskeeping/maintenance if they live in a condo or something).