"Mrs. Clinton is not the first government official — or first secretary of state — to use a personal email account on which to conduct official business. But her exclusive use of her private email, for all of her work, appears unusual, Mr. Baron said. The use of private email accounts is supposed to be limited to emergencies, experts said, such as when an agency’s computer server is not working.
“I can recall no instance in my time at the National Archives when a high-ranking official at an executive branch agency solely used a personal email account for the transaction of government business,” said Mr. Baron, who worked at the agency from 2000 to 2013.
Regulations from the National Archives and Records Administration at the time required that any emails sent or received from personal accounts be preserved as part of the agency’s records.
But Mrs. Clinton and her aides failed to do so."
That is pretty much the most minor and least relevant issue with Clinton's case.
Not really sure what the huge difference is in this case.