As an SME, You will have a smaller number of large clients, so you can genuinely deliver a personalised service and the time and attention of leadership.
Everyone in the core business will know about the background and status of each client company and act accordingly.
You survive on your good reputation - so this is central to your client relationships - in large firms this degree of dedication is not necessarily understood by everyone in the business.
For an SME, the leadership team are always involved in the sales and the delivery of projects. Everyone in the team will have worked together. In large companies, people who have never worked together, often get deployed on projects, the learning curve of getting up to speed on working and communicating effectively is at the client's time and expense!
Your fixed cost base are much lower.Large firms have layers of bureaucracy and protocols to try to leverage economies of scale. Your structure and size ensures that communication is fast
Poor performers and demotivated individuals can "hide" in big companies - or, worse still, go out to work on client sites and make them worry.