I'm guessing you're curious about why so many movies, tv shows, and games reference this aren't you?
Alpha Centauri is probably one of the most important star systems in the galaxy to us because it's the closest, only a mere 4.3 light years away.(yeah real close! lol) Another thing that makes this star system so important is it sports a G2 star which is basicly a sun just like our own except the one in the Alpha Centauri system is bigger. People refer to this star as Alpha Centauri A, she has a little brother named Alpha Centauri B which is a K1 type star and they have one other sibling named Proxima Centauri which is just a red dwarf many say. It's because of this systems G2 type star many believe there may be planets that have oceans and other life producing elements. It's because of this that alot of scifi writers will always want to reference this star system so their work will have a small basis of truth and possibility to it.
"Damn, where the hell do you think these little big-headed grey dudes keep coming from?"
"It's obvious they are coming from somewhere close, probably Alpha Centauri."