This makes rain break certain blocks. The blocks will be dropped as items, so if you're nearby, you can re-place them. Only a few blocks will break every now and then, but it's still an inconvenience, so it gives you a reason to build a roof.
You can configure the list of blocks broken, as well as how often blocks are broken. No blocks will be broken in biomes without rain (deserts, savanna, nether, etc.) but they will break in biomes with snow. Blocks that contain items will drop their contents. The default list of blocks broken has: Torches, redstone wires, beds, furnaces, blast furnaces, smokers, enchanting tables, bookshelves, lecterns, smithing tables, and brewing stands. You can add modded blocks, e.g. the machinery from Create.
Why would you want this? This discourages the strategy of placing down a bed, furnaces, etc. in the middle of a wide-open field, never bothering to build a house, and just sleeping every night to avoid mobs. In vanilla, if a player builds a warehouse to hold their factory, they'll feel like they're wasting their time, because there's no real reason not to just build it on open ground. With this mod, the warehouse will actually have a purpose.
For other mods that prevent sleeping in the middle of a field, consider Realistic Sleep by FoxMcloud5655 or Somnia Awoken by Su5eD.
For other mods that discourage boring, ugly but effective strategies, try Swan's Law by SwanX1, or Head Bump by me.
