I'll take a stab at shedding some light on some ASL minutae
The Delay while stopped usually has an effect on how you the player move your vech to impose bad DRM's on your opponents To Hit rolls.
AlanP says..
When entering the Brush hex, why not just declare 5MPs spent instead of 2?
The Defensive Fire DRMs are going to be the same, right?
Lets say the hex after the Brush hex is out of LOS of the AT shooting at you. (and your intention is to end up in the brush hex anyway)
If you state you spend the 5 MP's as you move in (your opponent will know you will end up in the brush hex and) the AT gun will wait to shoot at you until the 4th MP so as to avoid the extra + DRM mods on the to hit.
If you, state you spend the 2 MP's entering the brush hex your opponenet is not sure if you will end your MPH in that hex (you have 3 MP's left) so he might take a shot with the extra +DRMs and hopefully missing and losing ROF. Now you (moving the vech) can decide to stop, and delay in the hex or just state you desire to move into the woods thus staying in the brush hex in motion. or move to the out of los hex (a good idea if the AT gun kept ROF!)
Alot of compexity to draw out an opponents shot.. or force unfavorable mods, but its a part of the game alot of players enjoy.
Chris says..
What is the rational of only being able to delay once stopped?
Then, D2.1 one states that “A vehical may expend up to its full MP allotment…” this does not sound to me as an AFV must spend all his MP in a turn? What am I missing?
Not sure of the rational for the delay on once stopped, but the equivilant while moving is to expend more MP's than needed to enter each hex. It really makes for some complex and subtle interaction between moving and the DRM's you're allowing the defender on his Defensive fire shots.
Further down in D2.1 it says "...A vehicle which ends its MPh with MP remaining is assumed to use all those MP in that hex." So for all practical purposes the vech does expend all its MP's
So if you are moving out of los of an enemy and the last hex you enter is going to be in enemy los, you may want to delay or expend more MP's than needed before moving into the enemy los to impose the = DRM's on the enemys To Hit DR.
Hope this helped a bit.