Regression Testing is nothing but looking for bugs in code that used to work in past versions. It is not an easy task and so considered to be time consuming and need to be executed with each build. So if we address this task will allow to find bugs in code as fast as possible with minimal effort (automated!). This becomes more important the longer your product has been in production to keep customers happy. Bugs will happen and now way we can stop them we just want them to either be minor ones or issues limited in new code - not the old stuff that people rely on to get their job done till date.
It also acts to reduce the "drudge" work of manual testing and frustrated QA and Customer Support Teams. That work is also subject to human memory - as even if all the test cases written somewhere - are they all up to date? Are we sure? What happens if "human memory" on Leave :-)
Similarly automated regression tests also act to codify and formalize one's experience so,You don't lose the entirety of knowledge in case some one from the team move on as happens in this Dynamic Industry. So if we handle this will free up all resources at different levels which can do something "real productive". It also helps your team be "more proactive and less reactive". The more team spends fighting fires the harder it is to have a truly enjoyable work place. Not sure if you can enjoy this but I don't as it Stress out.
I keep detailed steps and possible available tools like from IBM Rational and various Automation Manager from IBM Tivoli and IBM Web Sphere with various work-flows in upcoming blogs in January.