A few weeks ago I broke my left elbow. "Good thing you're not left-handed" my doctor said with a chuckle. Well, I am left-handed so that's a big help. Now what?
As a true solo practitioner I had a brief moment of panic - how am I going to work with my arm in a sling? Now, I realize I'm not laying tile or playing the violin for a living but losing the use of my 
dominant hand for two weeks really slowed me down. I found myself in a situation where I could have easily turned to an assistant, if I had one, or even to a virtual assistant, if they could just SEE my desk and what needed to be done.
It occurred to me at this point that having my procedures written down would have been a big help. Something as simple as sending a fee agreement could have easily been handled by someone other than me, if only I could explain how.
That epiphany was followed by another - if I had been out of commission for longer than two weeks, could my business have survived without me? Maybe. Maybe not. Certainly not if I didn't have my systems written down for someone else to follow in my absence.
We all have our systems - how to bill customers, doing collections, following up on service, contacting potential customers, etc. But are they written down where someone else could follow them and execute the same thing without you hovering over them?
Putting your systems in writing serves several purposes. First, it allows you to delegate tasks you shouldn't be handling so that you can focus your energy on your core product or service. Ronda Henderson of Service Point said of business owners getting mired in administrative tasks, "any activity tied directly to revenue or relationships should be handled by the business owner. Everything else should be delegated." Second, it empowers your employees because they aren't just winging it and hoping they do it correctly. Third, it prevents you from becoming a micro-manager. Finally, and possibly most importantly, the process of reducing even your most mundane tasks to writing forces you to carefully review your methods where you may even find room for improvement.