Vanilla 1.1.9 is a product of Lussumo. More Information: Documentation, Community Support.
1 to 12 of 12
From the point of view of the general community I think the advantages of asking on MO is that the question and its answer are available on the internet for posterity.
From the point of view of the questioner the advantage is that you may get a good answer from an unexpected person. Furthermore, it seems plausible to me that you might get the answer faster on MO as more people will see it. The main disadvantages for the asker are that some people won't speculate as freely in public, and that the askees may not see the question on MO depending on timing (which may result in the question getting answered more slowly or not at all).
From the point of view of the potential answerers the main advantage is that you go to MO when you're in the mood to answer math questions, whereas you might be checking your email for lots of reasons. Furthermore, you're less likely to waste your time answering it, because you can see more easily if it's already been answered.
More specifically, I often find myself in the situation of wondering if I should email a fusion categories question to Pavel Etingof, Victor Ostrik, and Dmitri Nikshych (the first two of whom occasionally appear on MO), or posting it on MO. My experience is that more often than not my MO question gets answered by Evan Jenkins (or David Jordan or Pasquale Zito) before ENO even see it. That seems to me to be a better outcome for everyone. And if Evan, David, and Pasquale don't know the answer, then it's probably a hard question and I don't feel as bad asking more senior (and thus much busier) people.
In graduate school, you have the convenient thing that if you want to ask Prof. X a question, you can first ask one of X's graduate students. Often that'll get you an answer, but if it doesn't then you know it's a hard question. To some extent MO automates this process, where younger people with more time probably check MO more often, but then the unanswered questions stick around for other people to answer.
Someone even made a tag called [ask-johnson]
Ask your expert if they would be willing to post the answer on MO. If they say yes, ask the question on MO, then direct your expert to it. Everybody wins: MO potentially gets a new user, you potentially get answers from people you didn't have in mind, posterity gets a potentially valuable discussion easily searchable using Google.
I like to use something like Qiaochu's approach. I sometimes post a question on MO, and then email a link to the person I think might have an answer. This has a number of benefits:
If I'm really worried about wasting their time, I wait a few days before sending the link. If I haven't gotten a good answer on MO after a few days, it suggests the question isn't an easy one.