From a business law course I took long ago, a check is a formal type of IOU that businesses and banks have agreed to process promptly. In the 17th and 18th centuries, a paper promiss to pay some amount on demand might have made it's way from person to business to person across national borders for several years before being presented for payment, each person along the way discounting it a little towards the risk it wouldn't be paid. Now the movement from presentation to your bank account happens with electronic immediacy.   

Even though the check becomes void after some period, in the sense of your bank's obligation to honor it promptly when presented, the legal obligation of the writer to pay the specified debt remains. In Florida at the time I took the course, non-payment became a felony ten days after presentation of the check, but there wasn't any mention then about long delays before presentation.

Writing a check was as paradigm changing for mailorder businesses a century ago, as interet purchasing has been in the last 20yrs.

Jeff Smith, history nut