The Id DM brings up an interesting observation that minions exist and already do static damage, and based on that asks the question of whether damage calculations in general really matter. Responding to that particular case (minions) I have some observations:
- Regarding combat speed, it's true that regular monsters would benefit from the same reduction in rolls that minions do by eliminating damage; however, I think you can argue that there's going to be many more minions on the table when they appear, and so the benefit from simplification is a much clearer win.
- Regarding damage swing, I mentioned in my previous post that 4-6 rounds is barely enough for the law of averages to smooth out damage rolls and converge to the intended average -- and that's assuming your attack hits every round. As such, there really is a decent bit of randomness that can come out of combat (depending on how the damage expression is put together, with respect to die vs static bonus). Minions are even more likely than standard monsters to die after only one or two rounds, so they would tend to be even more swingy.
- I would actually argue that minions should not be allowed critical hits either, since the DM loading the board with minions means he rolls attacks a lot more, which means he has a much better chance of hitting a natural 20. It's essentially the DM equivalent of crit fishing.
None of this necessarily negates his observation, but I think it does demonstrate that minions are somewhat of a special case (if only by degree and not fundamentals).
What is the Real Difference?
As pointed out, it's clear Chris Perkins gains speed and efficiency from this modification, but the question is what he sacrifices by doing so. Depending on the power and monsters in question, maybe not much. As I asserted, dice add drama (the knowledge that you know what the average damage will be, but what about in this round, in this case)? For powers that get used very often this probably converges to the average very quickly; for big encounter/special powers though, it might be the difference between a crippling change of situation or a total flub. The DM doesn't know which is going to happen any more than the player, and that keeps it exciting.
Now, how much drama is created by a die roll depends a lot on the damage expression. Lets look at the charts Chris uses:
At level 10, 1d6+15 amounts to a roughly +/- 20% swing for each attack (from 15 to 21); meanwhile, 4d6+4 theoretically gives a much larger swing of +/- 60%. However, due to the nature of probability, it's not nearly that simple. Yes, the minimum and maximum values in that case are larger; but, due to the resulting distribution of values (which I'll go into further in a subsequent post) the average spread isn't really all that much greater. I don't have time to compute this myself, but I'd wager the range of the first standard deviation of 4d6+4 isn't that much wider than 1d6+15.
This may seem like a minor complaint, but lets take a look at the Brute Damage chart that Chris uses:
In keeping to his "two die" strategy he starts with a base of 2d6 instead of 1d6. This is odd to me because, from what I've read in the Dungeon Master Guides and from looking at the basic Brute monster design, brutes are designed to be much more swingy in their total results. Yes, they have large max damage potential, but there's a lot more luck in play when dealing with them (think fighting a trained knight versus fighting a giant). It seems to me that, at the least, Chris should just be using 1d12 in place of his 2d6 to preserve the random swingyness. As it currently stands, brutes are actually MORE consistent than regular monsters (or at least roughly as consistent) because they rely on 2d6 for their basic damage expression rather than a single die.
Yes, but what is Your Point?
None of this math really answers the question, though -- how is Chris' game actually different? What I would say is that it results in the DM being less surprised by an exceptionally high or low die roll, as well as the players being far more able to meta-game by knowing that monsters will do damage close to their expected averages. If you are running a tactically focused campaign where there are lots of secondary mechanics to deal with (especially at Epic tier) then this might not really matter that much. On the other hand, I think it could tend to suck some of the drama out of more leisurely games. As will all things in D&D it comes down to a matter of taste.