General Sir William Howe's Orders for the first of August, 1776 state: "The infantry of the Army without exception is ordered upon all occasions to form two Deep with the file at 18 inches interval, until further orders."1
This order served to accomplish two things. First, it increased Howe's front by approximately 150% even more if we consider the men of the third rank would have been absorbed to the first two ranks. Second, by introducing more "space" into the front, the chances of a projectile hitting a soldier (versus a "space") dropped considerably perhaps a lesson Howe learned from the Breed's Hill debacle?
When demonstrating tactics on the field, an open order of 18" (or one arms length) allows our re-created battalions to cover more ground, creating the illusion to the audience that the opposing armies are bigger than they really are. The down-side of this practice is that wheeling a battalion becomes a problem when at open order, as the ranks are too far apart to "feel" the inside man. This can be remedied by closing the line before wheeling, then opening again afterwards. This practice slows down the progress of the line, but proper formation was apparently more important than speed as hinted at by Humphrey Bland: "In all wheelings, either by division, or the whole battalion, the ranks are to be closed forward to close order, which is to one pace distance."2 Even though this excerpt is referring to the distance between ranks, it supports the idea that the battalion was tightened up before executing wheels.
1) General Sir William Howe's Orderly Book, 1775-1776, compiled and edited by Benjamin Franklin Stevens, London, 1890.
2) A treatise of Military Discipline, In Which is laid down and explained the Duty of the Officer and Soldier through Several Branches of the Service, by Humphrey Bland esq; Lieutenant-General of His Majesty's Forces, 8th edition, 26 March 1759, pages 11-17.
Like Howe, Bland also preferred open order: "The files are to be opened, the distance between one another, is one pace, or the distance of an outstretched arm; but that this may appear more plain, as soon as the the files are opened É those of the front rank to stretch out their right arms to the right, and if they can touch the left shoulders of their right-hand-men, they have their true distance".