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First of all, realize that Live View is not that sensitive. It's really made for bright scenes encountered in normal daytime photography. You're not ever going to be able to see a nebula or galaxy on Live view, but it definitely can be used for astrophotography by focusing on stars. How faint of a star that you will be able to focus on will depend on the aperture and focal ratio of the lens, and the camera settings.
Others who use it will let you know how really useful it is.