[lukevanoort]

Often you will put out the same amount of maximum pushing force in low and high gear because generally your wheel/tread material stays the same. (shifters with designs like 67's in 2004 being the exception)

The benefits of shifting generally are that:
1) The motors are loaded less in low gear
2) You can go very fast for covering ground
3) You can go very slow for accurate driving

Ideally, your wheels would slip at about 40A current draw from each motor so that you don't pop a circuit breaker and lose mobility; thus, with the most popular tread material (CoF 1.0) this means you (assuming a four chiaphua drive system) must go at most about 7-8 ft/s. 7-8 ft/s happens to work pretty well as a middle ground speed, but if you have higher traction tread such as as SBR Roughtop incline conveyor belting, that number becomes something more like 5-6ft/s. That is too slow for many teams; thus, they shift. The shifting then frees you up to have both ideal current draw in low gear and a blazin' 16ft/s high gear. As you can see building an effective two-speed drivetrain doesn't only consist of making (or buying) a good shifter, but also choosing the correct ratios for your drive system. (arguably, the latter is the hardest of the two issues)