If you are writing a book, it is always a good idea to keep a running list of terms you use in a way that may be outside the dictionary norm.
If you are writing fiction you can keep a running list of the way you spell names of people, towns, streets, etc. That way you will always spell them the same way and maintain consistency. That becomes especially important if you are writing about a fictional world. (Can you imagine J.K. Rowling trying to keep track of all the details of Hogwarts as she was writing Harry Potter if she hadn’t kept notes?)
Non-fiction authors often reference particular programs or processes they use in their work. Many times these are proprietary and may warrant registration as trademarks. Using the exact same form of the names of these elements becomes important legally if you want to claim trademark.
This list will be the beginning of a style sheet for your book. So just what is style sheet? First of all, there is a difference between grammar rules and style rules. You can get everything grammatically correct and still have a host of inconsistencies without a style sheet. You can think of a style sheet as something that establishes a standard to all the things that require a choice or decision. It also includes formatting elements – like how you will handle numbers and capitalization and one of the biggest points of contention, whether or not to use a serial or Oxford comma. (Not sure what that is? Just Google it and you will see tons of articles with people on both sides of this issue!)