Usually when I talk to people about keeping red wigglers I stress the importance of their basic needs, darkness, access to oxygen and moisture. I usually emphasize the need for moisture by pointing out one of the main characteristics that many people dislike about worms SLIME! Without moisture, they can't produce slime and with out the slime the poor worms are doomed. One thing that I usually don't get a chance to discuss is the real importance of that slime, not just for the worms but for those of us who use the worms castings as fertilizer in our gardens.
For worms, their slime protects them, as they wiggle their way through the soil (or compost pile) the slime helps lubricate their skin so they may slide past all those pieces of abrasive rock and wood and sand all the while serving as a glue to maintain the structure of their tunnels-at least in the case of soil dwelling earthworms. In the case of a compost pile or worm composting bin, this slime builds up on the organic material and the final castings helping to glue bits and pieces together. In the soil the tunnels that earthworms burrow remain intact with their dried slime scaffolding and allow water to pass through easily creating well draining soil that won't drown plants, but at the same time, as it is rehydrated it holds onto the remnant water longer, allowing plants to access the moisture later on as well as binding nutrients in place where plants can get to them instead of letting them wash away through the soil.
By utilizing the castings from vermicomposting we can also increase the amount of beneficial slime in our gardens. Although castings don't create the tunnels that help soil drain they do help glue together tiny bits of soil allowing the water to move around and in between them which still increases the soil drainage. In addition to this, I have read where the addition of castings to your soil can actually attract wild earthworms, this likely has something to do with the way that castings increase bacterial activity (good bacteria that is). The castings hold nutrients which help feed bacteria and as their population increases it attracts their natural predators such as worms. This all gets even more nerdy so I'll leave it at that for now.
So long story short, worm slime-although not all that popular with people- is of great benefit to the soil world and ultimately to the plants we grow. So if you haven't tried it yet, why not give it a shot?