Slarti........ the gear inches stay the same the difference to your ride is less drag from derailleurs and cluster(minor) and momentum from the back wheel reducing your effort to get over the top of the gear(major).

The common mistake is to use the bigger gears which duplicate dynamic load weight training which you can achieve with a good MTB workout rather than using the benefits of the momentum to increase your cadence and conditioning for higher spin and greater extension which equals greater muscular efficiency.