1) In-battle switching advances the character's status (eg. "Dark", "Silence") progression.  In other words, for statuses like "Dark" or "Silence" which are temporary and clear themselves after a few turns, you can simply in-battle switch the affected character back and forth a few times (~4-5 I think) and that would eventually result in the status removed, without losing the current turn at all (since you don't lose a turn by switching).  This effectively gives you a free way to cure those statuses.  Of course it doesn't work if the status is non-temporary.  Moreover, status like "poison" which regularly inflicts damage per turn, will inflict such damage during each in-battle switching as well.  I haven't tried "regen" status yet but I suspect it will likely behave similar, potentially giving you a free way to immediately and fully replenish your HP.

Of course, allies and monsters not involved in the switching are unaffected.

2) The stat boosts provided by Vince's special abilities (eg. Adrenaline, Meditate) will remain on the character post-battle (you can even see them in the menu screen outside of battle) if the character escaped during battle (either by "Escape" command or by Vince's "Flee" special ability).  On the other hand, if a character wasn't in battle when the battle ends (eg. you switched him out of battle, and then the battle ends by escape), he does lose those stat boosts he may have had during battle.  This is how I know one way or another, it is a bug and not intended.  The bottom line is that you can basically stat-boost up to 4 characters in your party before actually going into the next battle.  And yes, those boosts are saved (at least it look that way) when you save the game at a savepoint.

3) Arguable whether it is bug or just a sneaky trick intended for player to discover on their own, but because you can Escape from battle with an optional boss, if that optional boss has an item that can be stolen with Alicia's Theft ability, you can repeatedly steal and escape to get unlimited number of that item (until you defeat the boss of course or reach the max limit on number of items, or unless the boss is so quick and powerful, it kills your entire party after stealing without giving you any chance to escape).  In one sense, it's no different than the fact that you can do the same through random battles to accumulate such stolen items, so that's why I'm not convinced it should be called a bug.  On the other hand, the game (at the point I'm in so far, anyway) definitely depicts an optional boss as a singular character, unlike random battles where the monsters are presumably different members of the same species from battle to battle, and so it doesn't feel like you are stealing from the same entity with random battles.

Cerberus and Suzaku, the latter of which cannot be escaped from.