-How to properly scale the encounters with the party's strength level, taking into account that min-maxing can tilt the balance in favor of the players, but where compensating can increase the chance of random dice results causing a TPK. Maybe the Paladin min-maxed, for instance, but the Bard didn't, and if the ramped-up monster group kills the Bard right away the party may fall as a result. This is not just a week-to-week issue, but since many DM's plan encounters long in advance they often have to be retooled on the fly without undermining the narrative quality.
Min/maxing is exactly why I am criticizing the video game mechanics of later editions. When I first played, the DM wouldn't even let you level up without playing through a quick "training montage" to explain what skills you were developing. You couldn't take a new weapon's specialization without buying the weapon and finding someone who could teach it to you for example. Try to explain in narrative how you came to create a min/maxed character, and what that characters' motivation actually is. Is your party's only common ground really that they are each utterly devoted to true master of a single combat technique? Then why are they going adventuring again, wouldn't that distract them from their quest for mastery? Shouldn't they be annoyed with being taken away from training?
Video game mechanics, modular levels and modular skills are what have imported min/maxing into pen & paper RPGs.
On the old rules, you could turn an attack by kobolds into a level appropriate challenge if you added strategic and tactical elements to it. We used to penalize rules lawyers, with the new rules
every PC is a rules lawyer.
That was one of the great things about SLA, if you had a party full of combat specialists, you could always assign them public relations missions like speaking at a school's career day (the body count on that one was insane by the way
-How to create incentives such that the party will choose to pursue what the DM considers the main narrative. If the party is too powerful they may find ways to circumvent or even avoid the main story, which means the incentives and 'hooks' need to be balanced accordingly.
Well, honestly the best incentive is to make the story interesting. I never had any objection to PC's wandering off the beaten track, don't think any campaign that I was ever involved in stuck to one story in every gaming session.
I still remember being appalled when I read a DragonLance module, where it literally said that if the PC's walked any direction but north east they would encounter a group of mobs every 1-6 turns until destroyed. Why on Earth would anyone need that mechanic? If its that vital the players end up where you want them to be, then where you want them to be should be on their path no matter where they actually go.
In short though, the party could not be too weak or too strong other than by the conscious choice of the DM under the old rules, under the new ones PC's have too much latitude to control (and manipulate) the mechanics.
-How to assess exactly how hard the party should have to work for a success; this can range from making it easy for them to the extreme where some DM's actively want their monsters to win and enjoy seeing a TPK. One DM in my group has a trace of this latter, but still knows he must balance this desire against the group actually wanting to play his campaigns.
Again the problem with the new rules is that they encourage a DM to let the mechanics ruin game play, and they even back up the players in making arguments to that effect.
I mean there are game systems where the players are hopelessly outclassed (like Paranoia) and those where they can literally do virtually anything they want (Amber Diceless) that can be a ton of fun and balanced. Creating a rule system that intentionally is designed to create an unfun imbalance is criminal.
There are other factors as well, but these are some big areas where the DM needs a very good sense of balancing factors.
A DM does need a good sense of balancing, what they shouldn't need, is to "cheat" to undo game mechanics that are in the PC's complete control.
