It is important for an array of reasons. Irrespective of the what one feels about the moral aspects of his behavior, it is relevant because 1.) It puts him in a position to be compromised, 2.) It takes away the ‘moral high ground’ from him if/when he tries to use this ploy in attacks against Republicans, 3.) Remember what they did to Herman Cain. If you let them do that to us without reprisal you just invite more of the same.
Finally, when you are a politician living off the taxpayer's dime, you don't have the right to do whatever you want in your private life and not be culpable for it.
Excellent answer.