Above about 70mm, binoculars become a category of their own: mounted instruments that compete with small telescopes and offer something no telescope does, which is two eyes on the same object.
What two eyes actually gain
Observers consistently report seeing fainter detail with both eyes than with one at the same aperture, and the effect is real rather than folklore: the brain combines two noisy signals into a cleaner one. It is why a 70mm binocular can show a faint object that a 70mm telescope struggles with, and why owners describe the view as more immersive.
The sizes and what they need
Fifteen by seventy is the practical entry and needs a tripod. Twenty by eighty and up need a solid mount, ideally a parallelogram design that holds the eyepieces at head height while you swing them around the sky. Binocular telescopes, with interchangeable eyepieces and apertures of 100mm and beyond, are a specialist and expensive category.
The neck problem, which decides ownership
Mounted binoculars pointed high put your head in a position nobody can hold for long, and this is the main reason large binoculars stop being used. A reclining chair solves it entirely, and a parallelogram mount solves it better. Buying either alongside the binoculars is the difference between an instrument used and one stored.
Whether they replace a telescope
No, and they are not trying to. They will not reach the magnifications planets want and they will not resolve a globular cluster. What they do is sweep the Milky Way, frame large nebulae and clusters whole, and make an hour outside pleasant in a way a single eyepiece does not.
Questions people ask about binoculars
What are giant binoculars?
Binoculars above about 70mm of aperture, intended for mounted use and competing with small telescopes on wide field deep sky views.
Are big binoculars better than a telescope?
Different. They win on wide fields, on comfort and on the two eyed advantage; a telescope wins on magnification and on planets.
Do giant binoculars need a special mount?
A parallelogram mount is the usual answer, because it keeps the eyepieces at head height at any elevation. A sturdy photographic tripod works for the smaller sizes.