It really depends in my experience: I think I prefer IRC for more complex/specialized/niche topics.
Quick back-and-forth for details is very efficient compared to e-mail or postings somewhere if asking for details is really needed. Similarly, it feels more appropriate for really short questions.
The waiting isn't so much an issue if you have a stable IRC setup (or the channel has good infrastructure), but can be a problem for people that don't have that. Generally, "please ping me if you reply" works fine, and less active channels can be quite good at directing questions to the right person.
And a big thing is audience: if there's only a few people I think will know a good answer, asking in an IRC channel or on a mailing list they use is more efficient to get them to see it. On Stack Overflow I have the risk of not only having it to word in a way that the few people I want a response understand it, but also so that everyone else doesn't feel like it's a bad question, can only ask questions SO finds acceptable, and maybe the right people don't even look at SO, or don't see the question.
This obviously doesn't apply to questions many people from a larger community can answer.
Quick back-and-forth for details is very efficient compared to e-mail or postings somewhere if asking for details is really needed. Similarly, it feels more appropriate for really short questions.
The waiting isn't so much an issue if you have a stable IRC setup (or the channel has good infrastructure), but can be a problem for people that don't have that. Generally, "please ping me if you reply" works fine, and less active channels can be quite good at directing questions to the right person.
And a big thing is audience: if there's only a few people I think will know a good answer, asking in an IRC channel or on a mailing list they use is more efficient to get them to see it. On Stack Overflow I have the risk of not only having it to word in a way that the few people I want a response understand it, but also so that everyone else doesn't feel like it's a bad question, can only ask questions SO finds acceptable, and maybe the right people don't even look at SO, or don't see the question.
This obviously doesn't apply to questions many people from a larger community can answer.