As you all should know, the minecraft world is seperated into chunks. 16x16 areas that are loaded depending on how close a player is to them. If you have machines or plants or anything that does something in a chunk that is not loaded because there are no players nearby nothing will happen.
This mod adds a block called a chunkloader, when placed it will keep chunks around it loaded even if no players are nearby or even online. So now your plants can grow and your automatic quarries can run, even when you're not around.