The larger the field of view, the larger the area of the sky you can see. Likewise, lower powers used on a telescope allow much wider fields of view than do higher powers. There are several optical designs used for telescopes. Remember that a telescope is designed to collect light and form an image. In designing optical systems, the optical engineer must make tradeoffs in controlling aberrations to achieve the desired result of the design.
Aberrations are any errors that result in the imperfection of an image.
Such errors can result from design or fabrication or both. It is impossible to design an absolutely perfect optical system. The various aberrations due to a particular design are noted in the discussion on types of telescopes. It also reduces lunar and planetary contrast. It usually shows up more as speed and aperture increase.