Why would I suggest double digging your garden? There is one main reason you would do this… to produce larger crops.
Most vegetable crops love space, not really more top space, but root space. Plants love to send their roots deep into the earth searching for water and minerals. By double digging your garden soil the deeper your plants will grow.
The French intensive gardening program uses double dug gardens to plant more crops in less space. If you have your soil dug deep enough, many times you can space your crops half the distance apart as you would normally plant them.
Double digging means dig a trench the width of your wide growing bed. Then step into the trench and use a digging fork and loosen the dirt one fork depth. Back upand dig another row putting the soil from your second row into the first trench. Then repeat the digging with the fork. Double dig your complete growing bed this way. Yes it is labor intensive, but you will now have soil that is two shovel/forks deep.
If you really want to make your garden grow… instead of filling the trench with the next row’s soil, fill it with compost then add the next trench’s soil on top of the compost. This will give you a raised wide bed that is three units deep. So, this year instead of using the tiller to only dig your garden 4 inches deep… use the shovel and double dig that garden. You will be rewarded many times over.