This make it easier to take pictures in subdued lighting. More importantly, it makes the viewfinder brighter and easier to focus. If you use filters extensively and have a collection of them in one size, you'll want the new zoom to accept that same filter size if possible. If you are interested in taking close-up photos, check how the lens is used for macro work. A lens having continuous macro focusing is more flexible than one with limited macro focusing.
Zoom lenses are available in a wide range of prices.
The preceding points have a great deal to do with the price of a zoom lens. A more expensive lens will most likely be faster than a less expensive lens. It may have continuous macro focusing while the less expensive one has limited macro focusing, too.