What is the use of Stub Wings on Helicopters?
In addition to serving as support for weapons, we must have in mind that they're both quite fast for a helicopter - 335 km/h (208 mph) for Mi and 294 km/h (183 mph) for UH. At such speeds, even small wings yield considerable aerodynamic effects, just like in planes. From Wikipedia article we can learn that Mi's wings can provide up to 25% of total lift at speed and important stability to counter tendency to Dutch Roll.

Curiously, both mentioned platforms exist in wingless configuration. For UH-60 it's quite common, while Mi-24 had it's wings removed for breaking records. This hints that Mi-24 is much more dependent on it's wings than UH-60.