On page 6 under "Area Terrain Features", it mentions that bad going "slows the movement of, and is an adverse close combat tactical for, some foot and all mounted and may hinder shooting (see p.10).
On page 10 in the fourth paragraph it mentions "A hill's crest, a city or fort, or a 1/2BW depth of difficult hills, woods, oasis, dunes, hamlet, or edifice blocks shooting from and at and element base edge entirely beyond any of these".
So the going in itself does not affect shooting, but the terrain type can, and as you can see from above, even a gentle hill which is good going can affect shooting.
And as Jesse mentions, being in certain types of terrain could affect a combat outcome even though you might not get a tactical +/- to your die roll.
Yep, any element type can form into line in rough going.
If you go to page 8 at the end of "Player Initiative Point Dicing", it mentions "Command distance 20BW if entirely Light Horse. Otherwise, it is 8BW, but is reduced to 4BW for troops entirely beyond the crest of any hill, beyond a BUA or a camp, on a Difficult Hill, or in or beyond a Wood, Oasis, or Dunes".
So if you have an element in the hamlet or edifice its command distance is unaffected, but if it has the hamlet or edifice between itself and the General's element, then the command distance is 4BW.
Consider also how the Combat Outcomes are different in Rough Going. For example, my opponent (far wiser than I in such things) the other day cleverly --and safely-- moved a Psiloi element into a muddy PLOUGH feature to extend a TZ onto a Cavalry element of mine --a move he only would have made because the Plowed Field was Rough Going. Damned skirmishers!