The main benefit of white mirrors is that you can use wet-erase markers on them, which provides several major benefits:

• there are very fine-tipped markers available (they're intended for overhead slides, and the ink doesn't smear nearly as much), so you can write much more in the same space
• you can rest your hand on top existing writing, which again allows you to write more in a smaller area, and paradoxically makes revisions easier
• you can use "templates", where parts of the ink are easy to wipe off (dry-erase), but other parts are harder to wipe off (wet-erase). So you draw a grid or other "fill stuff in here" designator boxes with wet-erase markers, and use dry-erase markers for the stuff that you want to frequently erase.

There are smaller benefits as well:

• Easy to clean. The surface is less porous than whiteboard, so cleanup is easier and more complete.

HOWTO remove the mirror silver and backing paint

• soak it in toilet cleaner, or muriatic acid
• soak it in lye, or paint/varnish remover

HOWTO frame it

• cut a rabbet in the wood, and epoxy the wood to the glass
• use marine glue
• lots of glues work