People that do jumping on bicycles keep their seats lower. Of course, they're off the seat half the time, too. So mostly the BMX and mountain bikes that are ridden off road will have seats lower than what you'd want for normal riding.

If you're cruisin' round the 'hood on your bike, you may want the seat way low so you look cooler. That's fine for looking cool, but not good for actually riding long distances.

If you're young and healty, poor set position won't bother you as much. If you don't have hills or wind or need to ride 20 miles, seat position won't bother you as much.

For some reason, every old cruiser bike I've ever seen for sale has the seat just as low as it will go. The bikes look better that way, but unless all the riders are in the 5' range, that's a terrible way to ride the bike.

Consider this: You can walk around with your legs pretty well extended and can probably walk 20 miles or more that way if you need to. But bend your legs until you're 8" shorter and see how far you can walk that way. You get that same effect in bicycling. If you're just putzing around the neighborhood, you may never know the difference. If you're riding a ways, you will.