There can be many reasons why it is difficult to write what you want or need. We have experience of many forms of writing and can take your spoken words and transform them into a written text, whether it is a story, non-fiction, report, plan, application or letter. For many people, that is the start that they require – something to work on that can be improved and perfected by the editing process.
The extent to which you need any of these stages depends on the purpose of your written work. An informal letter or a menu on a blackboard doesn't need to be perfect. But if you have invested a substantial amount of time in writing, and are about to spend a substantial sum of money on printing or publishing, you should certainly have your work edited and proofread. Who will believe your business plan if you can't even spell? Who will enjoy your story when they can't follow what is happening? Who will understand your user's manual when they can't understand the sentences it contains?