When meeting with small business owners we are often presented with a network of computers that are each an island unto itself. This means that there is no single point for managing security and storage. Each computer must be managed as an individual. In every single case the organization has completely failed to secure their environments.
If you are one of the lucky organizations that have zero regulatory compliance concerns, do not access or store financials, and have fewer than two employees and computers then you might be able to get away without a server. Those organizations are few and far between.