There are cases when may not have the time to reply immediately to all questions (e.g. small team). In that situation common sense will tell you which ones are more pressing, I guess.
Going a little off topic, one thing I've been noticing that works pretty well (especially in agile environments), if you can afford it time-wise of course, is to have one person exclusively dedicated to support for a week. Then rotate to another person next week. That will both keep the requesters happy to get answers on time, but also the repliers, who can fully focus on other things when they are not "support person of the week".