the way to handle a bin and harvesting depends on what you're doing and your goals - most keep a worm bin to process their kitchen waste, so wouldn't really have to harvest at all really, unless the worms got so plentiful they overflow :)

if you're into growing worms or processing waste products, the bin will never decrease in volume, because you're constantly adding feed, and bedding too usually, so you'd harvest when the bin gets too full

the object of feeding in one area and waiting a period of time to harvest the unfed area, is simply so the worms have time to finish their job in one area and move to the food, making it easier to scoop some finished castings without having to sort too many worms out of it - it's not a matter of 'letting it decompose' as much as getting the worms out of your way - castings are "ready to use" right outta the worms butt!!

a good way to seperate the worms is to take one of those orange mesh bags that oranges come in, and fill it with fresh unfinished compost - good lumpy stuff that still has recognizeable bits in it, but is past any chance of heating - scoop out one edge of the bin and snug the bag down in there and in a couple weeks or a month a good percentage of the worms should be "in the bag", set it aside and scoop out the rest of the material and it'll be easy to find most of the remaining worms to put back in fresh bedding, and also dump the bag back

Bill

Yes. It also gives any cocoons that were in the former feeding area time to hatch and move elsewhere. This makes it easier to harvest worm compost to make tea or soil amendment.

The citrus bag is great for those interested in selling or gifting worms-- saves a lot of digging or hand separating.