Making your battery last as long as your laptop does is sort of a voodoo science and you'll get tips all across the board if you search the Internet for advice. One common belief is that leaving the battery on while the computer is plugged into the wall long term (days, weeks, months at a time) is bad for the life of the battery as batteries drain very slowly even when they are not being drawn on at all. Thus while plugged into the wall the battery is constantly going from 100% down to 99% or so, charging kicks back in and back to 100% in a continuos cycle. This toggle allows you to disable that cycle if you know your computer will be plugged in long term.
Personally, I look to the fact that many laptop manufacturers only warranty the battery for a single year even if you buy the extended 3 or 4 year warranty. To me, that says todays batteries really just don't last more than a year or two regardless of how you treat them. But that's just my theory.