I have no problems with rerolls and have always granted them when requested by opponents thus far. I have only had such request made a handful of times over the five seasons I've played in DL. I have likewise requested rerolls about the same number of times in that same period. I have had about half of my requests rejected; some players simply want to play on what's rolled and other don't want to give up a very favorable field terrain wise for them. Those games have almost always ended in draws.
From a historical point of view, it was very difficult to force an opposing army to fight. Armies often spent whole seasons maneuvering without ever drawing the enemy into a full pitched battle. There are plenty of accounts of armies simply staring at each other from favorable positions till one side decided to move off and the process repeated itself. Hannibal's campaign in Italy is a classic example of this. Competent generals were careful about selecting the spots for their camp and deployment. Better one's were move creative and innovative in their use of ground.
From a gaming point of view, FOG2 doesn't let you pick your battlefield; your dumped on a map and have to make the best of it with the troops you have at your disposal. You can pick where to fight on the field to maximize your strengths and minimize your weaknesses, but you're still at the mercy of some very random generation. In the extreme cases, you can end up on a map where you have next to zero chance of victory and even salvaging a draw would be a challenge. Now, while some might argue these situations are a good test of one's generalship, a challenge to be savored, in competitive play they are not particularly fair and should be minimized IMHO.
Allowing rerolls, I feel, reflects a competent general realizing this isn't the place to fight and marching off before getting entangled with the enemy. They reduce the odds of unenjoyable one-sided games or time-wasting draws that leave neither side happy. Players that refuse to grant them have no one but themselves to blame if the opponent hides in terrain or simply runs away the whole game.
In the tourneys I run, Chaos and Little Wars, rerolls are unilateral; you can declare one and that's it, a new map is rolled. Each player is allowed one and they can mutually agree to one additional. In the 7 seasons of play, I have not asked for or been asked for rerolls under these rules any more than I have experienced in DL. I have had one case where my opponent and I did the full 3 rerolls as we got really garbage terrain twice. I haven't had any negative feedback or situations reported to me by players so far regarding this rule.
Your mileage may vary
Karvon
Chaos Tourney and Little Wars Organizer, TDC VIII Bronze Age Coordinator. WTC US Team Hell on Wheels Captain.