I checked with the touringplans.com ticket price calculator and found out something interesting. It was after reading someone's message that they usually visit Animal Kingdom and DHS in the same day, because the lack of attractions means that each of these is a "half day" park. They visit AK in the morning and DHS in the afternoon/evening, finishing up with Fantasmic.
If you allocate 1 full day to each of MK and Epcot and 1/2 day to the other parks then the cheapest way to get your 3 days of visiting is to get a 4-day non-hopping pass and burn 2 days on AK/DHS. It is more expensive to get either a 3-day hopper or a 2-day non-hopper plus a 1-day hopper.
This I think is useful information for people on either a 3-day vacation or who wish to visit the non-Disney parks for the rest of their week-long vacation.
If you're visiting WDW for more than 3 days and you're planning to park-hop on only some days and not others, it may be worthwhile to play with the ticket calculator and find out if it's cheaper to get a longer, non-hopping pass and burn extra days when you hop, as opposed to buying a hopper for the total number of days. At some point it may even become worth it to buy an Annual Pass instead of a multi-day park hopper.