Can get a cheaper airline ticket by booking a reservation to one city but getting off in another?

Yes you can - it's called Hidden City Ticketing, and is most common on domestic flights within the USA. For example, United Airlines fly from St Louis to Manchester New Hampshire, with a stop in Washington DC. The cost of flying on a direct, non-stop flight from St Louis to DC is $435 with United. However, if you bought a ticket from St Louis to Manchester it would only cost you $171. If you were only carrying hand-baggage, it would be very easy to get off the plane on the stop in DC, not return, and save yourself a lot of money!