After so many years of being involved in SMB, I have seen many write a business plan. I have also seen many give up on writing one because the amount of work involved they felt was more than what they got out of it. However everyone I know who has done a business plan said that they got much out of it. I think it is not essential but its a good idea.
I warn you it will be a lot of work. You will be running back and forwards to your point of sale software to get figures, probably talking it over with many of your staff and others. In general the more you put into your business plan, the more you will get out.
In my experience, there are two major factors in people writing a business plan. The first is if some want to formulise their business, as they like to be super organised and the other if they are trying to get finance. In finance, it's great as someone who does not know your business can pick up your plan and see where you are at and where you want to go.
It is also an advantage internally as it makes everyone think on the same wavelength which is particularly important in retail as it is a service industry and unlike many other industries, the retail business really depends on many small facts like services, atmosphere, image, etc., For example, heaps of people can buy magazines in many different outlets, why do they come to me? Possibly I have a bigger range of magazines, maybe I give faster service, perhaps ...... ? Now how do you think this will be in the next few years?
If you decide to go ahead, the next question is decided if you want to do it yourself or get a consultant. As many people don't know the first thing about writing such a plan, some people use these consultants once and then as they figure out what these guys are trying to do, do it themselves. I would say you are looking at a consultant budget between $800 and $2,000 for a typical SMB business. The big advantage here is that they do have industry insights here that you do not, and their business experience will help you. As they write the plan, they review your thoughts. Plus finance people think more of their plans.
If you want to do it yourself, there are several good resources available to you from writing a business plan, for example, the Australian government has free business plans and guides here.
Generally many of the books, from what I have seen are way over the top, probably because they are really written with insights from large companies and organisations.
In all likelihood, the best solution is to use business planning software, if you are doing it yourself as it will guide you through each step of making a plan and do much of the work for you. You are probably looking at $100 to $300 although Enloop has a free service here which is very good. At the very least with this free version, you can test it out, and if it does not meet your needs, then at least you will have some experience and know more about what you do require.
Here are some really good points with using business planning software based on the cloud.
1) It is easy to change.
90% of it will be the same as time goes on but that 10% will change dramatically. With software, you can print it out now, close the book on last month, then examine what went different and store it away for future examination.
You can also edit your figures and see what effect it will have on your plan. For example, you might say: I am budgeting for $1 million-dollar turnover and $220,000 gross profit, then you might say if I drive the business and push it to $1.5 million so producing a $280,000 gross profit, what will be the effect?
2) As it works on the cloud, you can be anywhere and when you get the urge, you can work on it. This is not a small factor as you need to be updating your business plan continuously; whenever things change, monthly as you do monthly reports and yearly as you review and plan for the next year.
Probably the biggest disadvantage is that these software have standard plans so you do not have much flexibility if your business requires something different there will be problems.
Hope this is of help.