The same as compass, image stabilizer feature is most practical when using in marine, but also useful on moving cars or helicopters. It’s a mechanism that eliminates hand tremor and shakes to secure a stable image viewing. It’s like fixing a tripod under optical product without actually using it. Image stabilization is also useful when featured in hand-held optics with higher magnifications.
The only downside is the price which is several times greater than with optics without stabilization.