Clipless shoes & pedals and long distance
Clipless pedals let you pull up a bit and road shoes are rigid-ish, so you can get some more power from each turn (of course, you're using your muscles in a bit of a different way). This also gives a bit of a different pressure distribution than platform pedals (look at the layout of say, a Look pedal versus a platform pedal). In an off road situation, they prevent you from bouncing off the pedals as well. You can use them for going for long distances just fine -- in fact, thats where they're primarily advantageous (note that for riding long distances, you need to be sufficiently physically fit and have a sufficiently well suited bike, such as a well bike fitted touring bike -- if you don't, no shoe can help/hurt you). However, walking around in them can be annoying (there are cleat covers and other things for dealing with this) due to the cleat and the type of sole in most cycling shoes. Note that just because something is labeled mountain doesn't mean it won't work with road (you just need the same type of cleat and pedal). They do make one side platform one side SPD (a type of clipless) pedals for people who ride with regular shoes sometimes and SPD shoes at other times / are transitioning. 

http://sheldonbrown.com/shoe-pedal.html is good reading. 
http://www.rei.com/learn/expert-advice/bike-pedals.html is as well, though note that SPD is also available for road use. 

The most important thing is fit and knowledge of how to use them - you don't want to fall down while stopping or have uncomfortable shoes for long distances, so you may want to invest in shoe fitting when giving them a shot. Much like buying boots, you may not use the same size cycling shoe as you do sneakers (especially if you wear US 13 sneakers like me...).