So there are two main glitches I use in my runs:

1. Saving on the trigger of encounter and reloading the save in some instances allows you to skip the fight.
2. Saving after picking up item/opening chest and before the trigger of the encounter marks the encounter as already beaten.

The first one does not work in all the encounters, but from what I found you can skip most of the story-wise important fights that way.

It also works on monitor battles. I was wrong before.

Also as of right now I have no idea what determines the starting position of Joan after you save her from her death. Edit: Joan position in the battle is determined by her position at the end of previous battle.

I also exploit one intended mechanic of the game. In particular each fight will end as soon as all the enemies are dead. That means for example if there is a wave of enemies to enter the battlefield at the round 3, if you manage to kill everyone before that the battle will end before the reinforcements can arrive effectively saving a lot of time.