The change would mean that instead of throwing four pitches wide of the plate, the pitcher simply indicate to the umpire that he wants to intentionally walk the batter, and the batter would then be awarded a walk.
The justification is that:
1) It would speed up the game (albeit marginally - as there aren't that many intentional walks, and they don't take that long.).
2) It would save the pitcher's arm (again marginally), as it's usually not a super fast pitch.
Naturally, I am against this change as:
1) Sometimes pitchers miss with their intentional walks, and the results are very exciting.
2) Sometimes batters can reach pitches that aren't outside enough, which creates some awesome baseball.
3) Runners can still attempt to move down the bases on an intentional pitch, although it is rarely done.
4) Fans enjoy 'booing' during the intentional walk. Don't take that away.