N-Modal Gameplay

Note: RPG talk up ahead.

Scenario One: Single Mode

Let's say that you have a spell called 'Heal.'
Once, every 30 seconds, you can heal someone.

You fight a monster, what do you do?

Obviously: You hit him, and once, every 30 seconds, you heal yourself.

Scenario Two: Single Bi-Modal Spell.

Now take the same spell, but give it the option to harm *or* heal. So now we have a spell called 'Harm or Heal.'
Once, every 30 seconds, you can heal someone, or harm someone, but not both.

Now you fight a monster, what do you do?
Do you heal yourself? Or do you harm him and hope he dies before he kills you?

Obviously: You harm him until you're almost dead and you heal yourself.

Scenario Three: Single Bi-Modal Spell + Single Mode Spell.

Now let us add a new spell to your list of spells. Let's call this one 'Ice.'
You can, once every 10 seconds, slow the movement of someone for 10 seconds and do a little damage.

Now you fight a monster, what do you do?

You could:

Slow down the monster's movement continually, and harm him with your spells, while staying out of the monster's attack range.

-Or-

If we're about to die, we can slow down the monster's movement continually, and heal yourself with your spell before going back to hit the monster some more.

Scenario Four: Two Bi-modal spells.

Now let's add something new to our 'Ice' spell. Let's say that instead of slowing the monster down, it can be used to block the next hit the monster does to us, giving us an 'Ice shield', or it can be used to attack the monster

Now we could:

Stay in combat with the monster forever, using our ice shield to negate damage and our heal spell to heal damage.
Stay in combat with the monster, using our ice shield to damage the monster and our harm skill to damage the monster.
Slow the monster down and use our harm skill to damage the monster, like before.
Slow the monster down and heal ourselves if we are about to die.

Scenario Five: 4 Individual Spells

However, if we had these 4 individual spells: Harm, Heal, Shield, Slow...
we would have a very different game plan.

It is true that we could do all of the options above, but the *optimal* solution would be:

Shield ourselves, and harm/slow the monster we're fighting. If we get low on health, Shield, Slow, run away and Heal.

There are no decisions to be made when we have all 4 spells. We don't have trade-offs. There are no difficult decisions to make. There will be no difference between individual play-styles. There will only be optimal players and non-optimal players.

The result -- Restrictions breed awesomeness.

The restriction of only being able to use one of two modes for your spells every once in a while gives you the freedom to choose a style of combat you like. If you had all the spells available to you, you do have the choice of choosing a style of combat you like, except that choice would be either optimal or obviously suboptimal.

If the optimal solution isn't clear, or is balanced between the modes, then players have the ability to express themselves and it creates depth in skill usage. Knowing what skills to use when and knowing how it will constrain you later adds skill into the game.