As long time player of this kind of game, back when it was called Adjacent Attacks, I'll write a few of my thougts. Of course they are my opinion, and in no way represent the absolute truth
I think the most important pro of this kind of game is that it allows for real strategy to be developed. The way in which you organize and command your troops trully matters. In "normal" game, the most you can do is establishing a strong barrier, or stacking on a key region. In trench, you can actually develop a more elaborate strategy. In fact, there is no "single" strategy. There are several strategies that can work, and they depend on the player personality, the current situation and the map. For some situations stacking everything in a stack of doom may make sense. For other situations fighting in two or more fronts can be the way to go. Sometimes a player can sacrifice a few regions in one front to secure a bonus somewhere else, or finish an enemy.
In my opinion, escalating it's not the best way to enjoy those settings. With escalating at some points the map bonus and geography lose importance, and thus the strategy gets less important too. Specially the "split in half" movement that breaks the supply lines loses importance when your enemy is about to deploy 300 troops next turn... My ideal settings are No spoils (but Flat Rate is ok too) and chained reinforcement. Specially I find chained reinforcements so cool because it creates a single very powerful movement each turn, which become the right balance between the useless adjacent reinforcement and the too powerfull unlimited reinforcements.
At first I thougt that freestyle could work well with those settings, but I have learned through experience that with trench freestyle still favours the player who can be always online, so it's better to use sequencial and if you get bored waiting for your turn just join more games.
