A pair of binoculars with a zoom feature have the benefit of giving you the choice of many different magnifications on one pair of binoculars. The varying power is altered by moving a small lever near one of the eye pieces.
The main advantage of this is the ability to change from low to high power without changing binoculars. Unfortunately there are many disadvantages. Overall image quality is reduced, with a dimmer and less contrasty image. Field of view is also reduced.
Don’t be fooled by small binoculars boasting extremely high magnifications. The image will be very poor and hard to focus. Also with many budget zooms the collimation may be so far out you will not get a single image.
Despite many zoom binoculars being lightweight, you will also need a tripod to keep them steady at high powers.
Don,t let the above put you off. You can buy very good quality binoculars. Helios are a prime example of quality zooms that keep the magnifications sensible.