Many of the companies I have worked with over the years are very familiar with their competitor landscape. However, in this day and age the landscape changes very quickly.
Historically, the changes would have been a new entrant to the market who has opened their business in the local town. With the advent of social media and a plethora of different marketing channels to choose from, it can take no time at all for an unknown business to be taking some of your market share.
The key to defend your business is to be aware of the competition, big or small, and regularly review what they are doing. In many instances it is simply countering what your competition are implementing, so you have a voice and the communications you send out, enable you to to be heard in the most appropriate places for your business.