The result: The team of scientists were able to narrow the current range of scientific estimates about the effect of dark energy on our universe (usually denoted by the symbol w) by 30%. That result also takes into account data collected using other techniques: supernovae, X-ray imaging of galaxy clusters, and data from the Wilkinson Microwave Anisotropy Probe (WMAP). That's what JPL astronomer Eric Julio calls tackling the issue of dark energy from all sides.
Who cares how fast the universe is expanding, and why is that 30% significant? Well, if you know the rate of expansion, you can deduce the shape (geometry) of the universe, and that shape offers vital clues to our cosmic date. Or, as lead author Priyamvada Natarajan of Yale University put it in the official press release: "The content, geometry, and fate of the universe are linked, so if you can constrain two of those things, you learn something about the third."
See, matter curves space and time around it and gives rise to what we recognize as gravity. The more matter there is, the stronger the pull of gravity, and the more space will curve – making it more likely that expansion will halt and the universe will collapse back in on itself in the antithesis to the Big Bang, dubbed the "Big Crunch."