You can't grind.
Dead enemies stay dead (no random encounters, 99% of all enemies are visible on the field).
Yes, the game has anti-cheat systems in place, in case you are overleveled.
Which simply means, reaching a level you simply couldn't have reached naturally at that part of the game.
But you can use an editor and edit stats, without affecting the level, as the game doesn't care about how high your ATK or DEF is.
That being said, the game detects if you won an unwinnable fight, which gets punished.
And the game detects if you defeat some specific enemies too fast.
You must be registered to see the links
Read with caution, as it is kinda spoilery.
It is encouraged to defeat every enemy, as experience and money are finite.
Don't worry too much about "defeating some enemies at a later time".
Some people make a big deal out of the fact that chars miss out on experience if you defeat enemies without getting the chars first.
It doesn't matter much, don't sweat it.
Also, everyone in your party gets the experience, not just active members.