I've ridden tandems with single/same-side drive but, again, all of our tandems use cross-over cranks.
Originally Posted by tandem_dude
1. When building a tandem it allows you to use a pair of standard triple cranks vs. buying a tandem cross-over crankset. This pretty much means you can use any single bike triple cranks that suit your fancy. For example, off-road tandem folks who opt for the Rolhoff hub can use a pair of Shimano XT cranks.
2. It reduces wear and tear on the stoker's bottom bracket by eliminating the torsion loads that run through the spindle which is being pulled forward on the left side of the tandem by the captain's pedal loads, while the right end of the spindle is pulled backwards by the drive train loads.
3. It puts all of the drive train components on the right side of the tandem, leaving the left side "clean".
4. It eliminates one timing ring and a crank spider on conventional timing cranks.
5. It draws lots of attention because maybe one out of 1,000 tandems are set up this way, although this could be a negative to some teams.
1. Running a triple with single/same side drive can get tricky and is usually best left to the cross-over crankset.
2. It puts all of the frame bending loads on one side of the frame... probably not a big deal but, heh, it is what it is and some builders make a big deal about boom tube deflection. This configuration just moves it over to the same side of the bike that's already loaded up between the rear axle and bottom bracket on the right side.
3. Dropping your drive train off the middle chain ring into your timing chain get interesting.
4. If you decide you really need a triple or want to run a kid-back you will end up buying a tandem cross-over crankset.
Anyway, that's just some of the things that come to mind.