The simple answer is YES you do need a business plan!

The term business plan gets thrown around a lot, and means different things to different people. Often when people talk about needing a plan to secure funding etc, they are actually talking about a business case, not a business plan.

A business plan is effectively your roadmap. It should outline the steps you are going to take in order to meet your objectives and strategic goals. It should contain key activities and programs of work, measures, milestones and depending on the size of your business who is accountable to deliver what and by when.

As a business you should be monitoring your progress against your business plan, very regularly (at least quarterly, if not more frequent. Exactly how frequently depends on the nature of the business). As a business, your business plan is the map to your success, and defiantly not a set and forget document.

A business case on the other hand (the document used to try and secure funding) is really about trying to encourage investment in your business. It is almost a sales pitch, and will be more focused on the risk / reward profile of your business (or specific initiative) and is not a document that will help you manage your business

Great question. A business plan is almost always required if you are seeking funding from a traditional bank or government grant program. Some investors (both Angel Investors and Venture Capitalists) may require or desire seeing one as well.

I would say that if you are not seeking traditional funding options to bypass the traditionally long business plan in favor of a 1 to 2 page Business Summary with a short 10 to 12 slide presentation. The 1 to 2 page document should be written like an Executive Summary (which is typically the first part of a traditional business plan). This document should contain high level details of the business as well as what you are accomplishing and what you will be accomplishing soon. Also include the amount of money you are seeking (if you are seeking funding) as well as what you plan on doing with the funding (more detailed breakout - hire people, marketing, advertising, etc.).

The presentation should be somewhere between a typical pitch deck and a business plan. Focus on your Unique Selling Proposition (USP), how you are different from your competition, and how your current customers (or tested customers) are responding to your business.

These documents can help other team members better understand where you are and where you are going. They can also help you attract media and press about your venture. Also if you are looking to do some crowd-funding this information will help you get your message across from day one.

I haven't revisited my documents and presentations as often as I probably should or even as often as I would like to, but I do believe revisiting them can be beneficial to see if goals have been met or changed and to see how your venture is evolving.

easy answer, Yes. A business plan isn't there to sell your ideal to an investor. It is there to ensure you are on the right track. A business plan will help you work out what your pros and cons are. What issues could appear, how to solve them. Your target market. KPI's to check if your on track. 

A business plan is just that. Without it you just have an idea.

Your building an App. So what is the timeline for Dev, what is Beta release. Who is going to take part in the Beta release. How will you measure success of Beta release. Once Beta is completed. How much time is allocated to more dev prior to launch. When you launch, how will you launch. 

Big part of your business plan is dev in the tech world. Do you have a Gant chart to help maintain a schedule for your projects? Pretty sure you would. A business plan is your "Gant chart" for your business.

I have setup businesses without a business plan, very quickly worked out that I needed one. A business plan is not a boring doc you write to make something official. It is a plan of attack.