Concern: I will be chugging health potions all the time!
Result: Nope. In what we call a "popcorn fight" (a small fight that is not meant to really threaten the party), I rarely have to use a potion at all. After a normal-level fight against wandering creatures (a single large enemy or a group of normal enemies around my level), I usually use one or two potions (total, not per person). During a particularly difficult plot-related fight (which will usually give me a chance to rest afterward), I might use one or two during the fight and then one or two after the fight, for a total of three or four.
Now, to be fair, I found initially that I WAS taking significant hits and drinking a lot of potions—in earlier areas, fortunately, where the game is forgiving about letting you heal up. Within a few hours, though, I had gotten to the relatively low level of potion use I described above. Here's how:
Barrier: If you have a mage in your party, and you SHOULD have a mage in your party, this single spell covers you a lot of the time. I've seen people say that it makes you immune to damage for a short time, which isn't really accurate. Instead, think of it as giving you an additional health bar that the enemy has to take out before they can actually damage your normal health. (For Mass Effect players, think of shields or biotic barriers; for d20 tabletop players, temporary hit points.) Barrier costs little mana and covers a reasonable area. Cast it at the start of the fight, and everyone on your front line has an additional health bar to soak damage.
Guard: Guard is similar to Barrier in its function: an additional health bar the enemy has to take down before they can damage your character's normal health. The key difference is that you gain guard from any of several different warrior abilities, not from a spell. You almost always only give guard to yourself, and you get less guard from each ability than you get from the Barrier spell, but there are several abilities that give you guard, and they stack.
Here's how most fights go for me:
Cast Barrier on the party (or at least on the frontline combatants)
My party tank (currently Cassandra) uses one of her abilities that generate guard for her
Yes, guard and barriers stack—enemies have to break Cassandra's barrier AND guard before they damage her health
When Cassandra's barrier gets broken, have her use another ability, so that her guard goes up even further
If enemies are still up and dangerous and everyone's barriers are dropping, I make a snap decision about whether I want to turtle up (have folks use defensive moves to withdraw) or power through (keep hitting, with the expectation that I'm using potions later)
The rhythm is definitely different from "use healing spells during the fight," but I personally like it. Rather than forcing a grind, it rewards planning, where "planning" can be as simple as "use the ability that gives everyone something like shields, and the other ability that gives your warrior something ELSE like shields that stacks with the first thing." And with tactics set for party members to use their abilities normally, "planning" on easy fights looks a lot like, "Have a mage with Barrier in the party, and he or she will slap that bad boy on you as soon as you see the enemy. Just let Cassandra do her thing. That lady is like DA:O Alistair. She just. Does not. Die."