Stars twinkle as a result of turbulence in the atmosphere. A sky stuffed with twinkling stars may be pretty, but it’s the worst scenario for viewing the sky. The temperature, water vapour, and density of the different layers of the atmosphere are constantly changing, and as the beam of light from a star passes through the air, it is refracted irregularly as a result of this. Thus, the twinkling effect is created.
If you tried observing with a telescope on such a night, the image wouldn’t be very clear; it would constantly appear to dance or shimmer. In fact, the more brilliant the shimmer, the more likely it is that a storm is brewing (as the atmosphere is more chaotic during storms).
While summer nights appear hazy and there seem to be fewer stars in the sky, they are the best time to capture the best telescopic views, as the atmosphere is much steadier.