See image below.
The pre-battle screen (left panel), playing as the French, shows Dorsenne and Lauriston as +2, which I guess means that they will arrive in battle round 2, as the ’Battle Completed’ (right panel) shows these units arriving in round 2, incidentally, so does Fresnel for the Austrians. This should be the effect of ‘To the guns’.
I have all the French corps set ‘To the guns’, but it can have unexpected effects, as units tend to follow the enemy, rather than stick to the ordered objective. This has happened several times and may be the reason that DAVOUT’s artillery was lost, isolated on the road, as other units chased the Austrians, on another route rather than take the road to the ordered objective.
I am thinking of ‘To the guns’ as a use your own initiative button, which can have unforeseen circumstances, so use with caution and don’t be surprised if some units head off on their own.
I had not seen this in previous AARs playing as Austrians, because under house rules I am not using ‘To the guns’ for them.

This is from the AAR which I have not written up yet.
This is a massive win for the French, NAPOLEON is in command with bonus, he has the Guard and the Austrian units may be damaged from several unsuccessful battles in the previous turns, but it doesn't work out so well for the Emperor in the following turns, which shows the variation in the game, as circumstances change.