The smaller the angle, the greater the resolving power. This is a theoretical resolving power in fact, in the visible range of EMR, images are blurred to sizes of about 1 by the Earth s own atmosphere this is called seeing . Thus, building large optical telescopes does not, in general, improve one s resolution. In general, astronomers are not interested in magnifying power since even with infinite magnification, you could never see detail smaller than the resolving power and seeing allows. Outside of Earth s atmosphere, so images are diffraction limited and not affected by seeing.
Disadvantage is the enormous cost.
Instrumentation no one looks through telescopes anymore.