In Germany, there is some limited funding available for unemployed persons who start a business. I know a number of people who have take advantage of this Überbrückungsgeld (literally: "bridge money") in the past. One of the requirements for getting this funding is to write a business plan and have it approved. Unfortunately, many people cede the responsibility for this task to their tax advisors, who do a minimum of documentation to satisfy the formal requirements of the government's employment agency. Very little thought, if any, is give to real planning for the business ahead.
I am not a slavish follower of schedules, to-do lists, Five Year Plans and the like. But I have always found that written goals provide a point of orientation that at the very least give me a better appreciation of the journey, even if I go another way. And when things start to get busy, a written business plan helps me to keep focused and provides me with a basis for systematic changes of course where needed.
A few years ago, I wrote a short article on ProZ describing my approach to business plans for translators. In actual practice, the plans I have produced in this way can be rather large after including financial statements, certificates, testimonials, etc. The full version of the business plan was a means for me to collect information which I subsequently excerpted for various purposes as banks require documentation for loans, prospects requested references or a potential employee needed an overview of what we did at the time. It is possible and probably desirable to do shorter summaries in most cases, but with no roadmap at all, distraction and drift are threats that are all too real. After a recent business reorganization where I ended a partnership and started a new and somewhat difficult to define business relationship, I found that working without a detailed outline of issues and priorities considerably complicated the transition, and that mistake is now being rectified with all due speed and effort.
I think of the translator's business plan - or any useful business plan - like a good map that points to the most likely path to follow but also allows for and suggests alternatives when obstacles are encountered. It should be a "living" document, a sort of dynamic diary that is adapted to reflect the changes in your business and its environment.