When getting ready to go to the airport for the next family vacation or business trip or just to pick somebody up that is arriving, there are types of parking for each.
If going to take a week or more family vacation than it will be important to make sure to park in the long term parking or to take a taxi or shuttle to the airport to get the best deal.
Secondly, if traveling on a business trip for just a few days than look into the short term parking to find the best deal in parking.
Lastly, if just going to pick someone up then look for the short term parking also. More info: seatac airport parking