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Increased characterization will provide interesting theoretical optimization challenges, reduce the strategic options of the DM, and make it more likely for you to actually play a game session.

I'm actually going to expand the question slightly:

What are the benefits of increased characterization?

As stated, any attempt at characterization theoretically creates more in-world reasons for the DM to attack you. Be it a character goal, alignment, or what have you.

We must address three things: The opportunity cost of characterization to the DM, the opportunity cost to the player, and the benefits to the player. In many ways, I will be drawing on my character optimization paper here.

What it allows the DM to do and not do

An alignment, or characterization, allows the DM to structure the world and opponents to more closely align with the character's goals. If the character is a good character desiring power, a kindly (but not too deep) DM will present evil opponents inhabiting the world to provide a guilt-free slaying experience, because that is, apparently, what good people do in D&D.

But, more to the point for an optimizer, it constrains the DM's decision space. Given that the DM can place any enchantment on a monster and that consecrate and the various $antiAlignment spells exist, a monster who takes those spells cannot take others. Given that you know the more likely set of spells taken/enchanted by monsters, it becomes trivial to then prevent those spells from providing any utility to the DM through strategically chosen counter-spells.

To summarize: characterization choices you make restrict the "logical" (in terms of story) courses of action the DM is likely to take, making it easier to foil those courses of action. Given the non-optimal nature of anti-alignment spells and effects, you can entice the DM into sub-optimal "play" through increased characterization.

Opportunity costs to the player

The act of characteriazation, be it through alignments or a more nuanced moral code, is the act of articulating and playing a series of prescriptions and proscriptions: acts that you would prefer to do and not do. Theoretically speaking, this absolutely limits the gross decision space of possible actions you may take. However, the addition of structure via pre- and pro-scriptions into your decision space allows for more nuanced choices, strategies, and options.

Structure, while nominally forbidding actions, creates a logical framework that improve the coherency of the action space as a whole, while allowing "forbidden" actions, through an act of reframing, to both be allowed and character-affirming.

Benefits to the player

As an optimizer, but as someone who enjoys RP, there is an interesting dichotomy in play. The problem I all-too-often finding myself having is weighing otherwise equal mechanical choices. By creating a narrative framework and narrative requirements, I find that certain choices by their appropriateness to the narrative, become more attractive.

Though, while looking at your bio, I found this:

I like to optimise my characters for maximum efficiency, but unfortunately I’ve done this to the point where no one will GM for me anymore :(

The best benefit of characterization, and the best benefit of choosing alignments to support a narrative structure is: people will be more interested in playing with/DMing for you.

A theoretical character that can theoretically beat Pun-Pun a level before he hatches is all well and good, but it still lacks the necessary social prerequisites that transform it from a fascinating mathematical exercise into a game. By intentionally creating restrictions and requirements for your characters, you can present yourself with a greater optimization challenge (which I personally find more fun then bland already-solved puzzles of max damage), and allow for opportunities to bring these theoretical abstractions into play.

Edit (based on reflection):

Weakness is a poorly framed statement.

I’m a power gamer at heart, and I cannot bring myself to play characters with weaknesses. The only time I will consider playing anything other than TN is when I’m rolling a Paladin.

This statement, more than anything, is a framing problem(caution, SEP). As alignment is representative of characterization, and you view characterization as a threat to optimization, you can then weight your ontological values placed on the (trivially counterable magics and items) such that they prohibit you from making any other choice than the one you just made.

Asking you to update your fundamental belief system based on an answer is silly. And while I (think I) make persuasive comments above vis-a-vis characterization, if you don't want to do it, you don't have to.

Here is some logic to reduce your confidence in your belief of true neutral's superiority: