Engineer can shoot further and deploy sentries in a larger area.
~ Official Description
Larger Service Area is the second upgrade of the second path for the Monkey Engineer. This upgrade increases the range of the Monkey Engineer to near that of a Super Monkey with the Epic Range upgrade.
Experienced players consider this upgrade not only a money sink, but also a detriment to its power. Sentries will be deployed further, which at first may seem to cover more area, but will decrease the strength of the sentries due to less sentries shooting at one spot.