I have never seen "IANAL" ... in fact I just figured out what it meant (my bad). Personally, I almost never use an additional disclaimer. However, there have been times when I've seen really good questions that appear to be seeking actual specific legal advice. As an attorney, the rules of ethics necessitate that if I give legal advice to someone in a back and forth (Q & A) manner, without creating an attorney client relationship (carrying with it all sorts of duties and privileges), it is incumbent on me to ensure they realize, without question, that I am not creating that type of relationship. Because of that, there are times (not often) that I have felt compelled to explicitly make clear to them that this is what I am doing.
This is especially important when I am giving an answer that (I think) fully addresses their question, but as a lawyer I can clearly see that the question they asked should necessitate a whole host of other questions that are relevant and important to their particular issue, and that I would obviously address with them if they were my client. But since they aren't, I don't know if they've already dealt with and have recognized those issues, and it's not really my place or the correct forum to ask.
Since someone can click on my profile and read that I am an attorney, if I feel like they may rely too much on my answer/advice without knowing that a whole bunch of other issues exist by mere virtue of my profession, and I want to make sure they know not to rely on that answer alone, I have added additional disclosures. I apologize if this has ever offended or annoyed!
Just a note: I think that the specific disclosure about not relying on the advice on here could be more visible than it is. Especially for this particular community dealing with legal issues, this could be more important, as opposed to other SE communities where it's not as relevant. And since the APP doesn't have the disclosure at all (at least not that I've seen).
If that additional disclosure bothers people, generally, then I'm not sure what the best course of action is, short of either making a rule against it, or making it their problem to just deal with. I can see how it could be annoying if someone puts that every time they answer a question.