To answer your question, sustaining a competitive advantage is key to the success and longevity of any business of any size.
Research and real world examples show businesses that do not continuously “sustain a competitive advantage” do not survive in the long term (assuming they had an advantage to begin with). An example is Blockbusters and Netflix. Netflix adapted their competitive advantage to streaming (an emerging technology at the time) while Blockbuster did not adapt so no longer exists.
This is even more relevant today in the global digital world we live in because there are new technologies released every 12 to 18 months providing you (and your unknown competitors) with new ways to excite and entice customers over and over again. If your competitors have more exiting products/services/pricing your customers will move over to them leaving your business with lower revenue.
Be aware there are different types of competitive advantage. Technology in the example above is the dynamic kind, one of several key areas for any business of any size to find a continuous competitive advantage.
As Ginni Rometty, Executive Chairman of IBM says "You've got to keep reinventing. You'll have new competitors. You'll have new customers all around you."
If you like, you can learn more about business and technology management here.