When Lew Wallace was informed he was on the wrong road he performed a counter march so that his best brigade stayed at the front of the formation. The first courier to Wallace had said that the Union was doing well but by the time the courier arrived that informed him of the better route (or rather the only route now available) the day had turned against the Union. Wallace was now informed that he might have to rescue the rest of the army from a dire situation. If the army was really in such a dire situation it makes sense to put the best brigade at the head of the column. If he would have had to fight his way across the bridge or go into combat soon after that he would need his best men up front.
His other option was to about face the entire division. If Wallace had been marching straight into combat it would have been important to have the best brigade attack first. If he had performed an about face he would have arrived on the battlefield a little earlier but probably not in time to take part in the battle that day.
Since Wallace stood little chance of seeing combat after taking the wrong road the reverse march does not rate as a critical decision. The net result of Wallace taking the slower method of turning around was just the time lost. Wallace cannot be faulted for his decision to counter march because he had just been told that the fate of the army might rest on his shoulders. Having the best men up front was now more important than the time saved by about facing the entire division.
I would also like to add that even though above I refer to Wallace being on the wrong road I'm not in total agreement with that, see the most recent post about Wallace, as Wallace knew of two roads from his position to the main encampment. One road had already been selected as the route Sherman would take to help Wallace. The shoe was on the other foot so Wallace took that road. Once Sherman has had to abandon that bridge Wallace's route is the worse option. Perhaps if the first courier had said the situation was particularly bad Wallace would have taken the route that put him behind the Union army and would have allowed Grant to place him where ever he needed him. Overall I think Wallace has taken too much grief for decisions that were not bad decisions based on the info he had.
Another thing to note is that, from what we can decipher, Grant's orders were not crystal clear. Everyone was learning on the fly. In the future Grant's orders will be much clearer, this is one lesson he took from Shiloh. If Shiloh had been an 1864, or even an 1863, battle it would have been fought much differently. I don't mean entrenchments and the like, just that command and control issues would have worked much more smoothly, orders would have been better. Veterans at all levels would have behaved differently. This is one aspect of Shiloh that interests me, the rawness of the troops and commanders and how they all acted. A great book on this aspect is Seeing the Elephant: Raw Recruits at Shiloh by Joseph Allan Frank & George A. Reaves.