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The implication of Hubble's Law is that the universe was, at one time, in an incredibly dense state. In other words, it implies the Big Bang. Additionally, since some galaxies appear to be receding from us faster than the speed of light (impossible according to relativity), this means that the universe ITSELF is expanding and it's not merely the galaxies moving THROUGH space (the galaxies are just getting dragged along for the ride).

A practical use for this is to determine the distance to galaxies. By determining how fast they're moving away, we can use the law to infer their distances. NOTE: for galaxies in our own cluster in which gravity overcomes the expansion, this approximation falls apart.

Another use makes use of the Hubble Constant (one of the terms of the equation). By taking the inverse of it, and manipulating the units correctly, the distance units will all cancel out, leaving only time units, which gives the age of the universe.

The Hubble Constant is also an important parameter in cosmology. Ironically enough, the Hubble Constant is not actually constant (although it is for our given time) through the history of the universe. By studying how it changes, astronomers can determine the eventual "fate" of the universe.