What does it mean to play suboptimally?
To use an example from last week's column, not optimal (oh, cripes, I'm doing it again) is making choices that aren't as effective as better options, yet you choose them because they feel right at that moment, like speccing into Hallowed Ground to boost your Consecration. The thing is, while there can be corner cases where Consecration is so critical that an extra 45 to 72 DPS would be a huge help, by and large, the wasting of two talent points enhancing the spell is nearly guaranteed to be a huge disservice to yourself. You'd be far better off dropping a golden puddle sans those two talent points sacrificed on the altar of "it feels like it works better."
Non-optimal play can mean making choices with a poor return on investment, in short. In terms of damage and threat, I'll explain in a bit why being suboptimal in that regard can hurt a group, when coming from a tank.
Another example: Some people worship on the altar of total damage reduction (TDR) and use that as a metric of a tank's effectiveness. Many tanks (some the best in the business) would counter that the best use of a cooldown is when it's most needed to prevent a spike in damage, rather than randomly to bring down some number on Recount. A tank could have mountains of TDR over the duration of an attempt, but if he fails to use his cooldown at the most opportune time, eats a spike, and dies, what good is that number?
Behavior like macroing Holy Shield to Crusader Strike is just about always suboptimal, because it can lock you out of the ability when you might need it most. The only exception to this is probably Ultraxion, where such a macro saves you the micromanagement of hitting Holy Shield every time it is available at half the cooldown it normal has. But again, this hearkens back to optimal play as a shifting but steady constant. In this case, that macro can help you keep up an ability that needs 100% uptime, which improves your survivability. Otherwise -- terrible idea.
What's the point of optimal play?
For starters, when you play optimally, you make the lives of those you play with easier. Doing your maximum possible DPS without sacrificing any survivability means that the DPS players have a higher initial threat ceiling for when they're pre-potting and popping cooldowns right at the start of the encounter. It means that your contributions to the raid's total damage output allows in turn less tight DPS requirements from the rest of the raid (perhaps allowing your team to surpass that gear check). And it means that you require much less strenuous healing, allowing the healers to have free GCDs for the rest of the raid.
When you play optimally (again, this includes your talents, gear choices, and the like), you can push the upper limits of your survival to the point where attempts learning a boss last that much longer. Every percent of the fight you can keep yourself further alive through is another percent that the raid will be able to learn and that much quicker the raid will be able to learn and conquer the encounter.
As I said, it's an act of respect toward your fellow raiders or groupmates. You're not making them expend extra effort to pick up the slack that are generating. In a game where people seem to care less an less about what other players think and how they feel, paying such a kindness is a rare and valuable thing.
Likewise, when you are optimal with regards to your threat output, you can focus more so on your personal survival. If you can suffice with the proper talents and glyphs alone, then hit and expertise gear becomes all the more meaningless, and valuable itemization -- gem slots, enchants, gear choices -- can be funneled into mastery, stamina, avoidance, or what have you.
In a world where threat is generally easy mode, why would you ever elect to boost it at the expense of your survivability when your own personal damage contribution doesn't matter? Every fight isn't Ultraxion, so there's really no general occasion where one must absolutely be hit-capped and expertise soft-capped (unless we're talking serious farm content -- but even then optimal play has its place ... no one wants to wipe on farm).
Ultimately, if threat doesn't matter (and it generally doesn't, with correct play), why would one not choose to do threat right with minimal investment than doing it incorrectly with far more? The former is optimal play through rotation, glyphs, talents, and so on, while the latter is doing things like wasting talent points on Hallowed Ground and wasting itemization on hit and expertise rating.
Lastly, there is a certain satisfaction to playing at the peak of your potential, is there not? That euphoric high of giving your all and reaping the rewards should be reason enough for all to be given.
The Light and How to Swing It shows paladin tanks how to take on the dark times brought by Cataclysm. Try out our 4 tips for upping your combat table coverage, find out how to increase threat without sacrificing survivability, and learn how to manage the latest version of Holy Shield.