I never like to discourage 'too much' information because frankly 'end users' don't know what they need to tell us in support (that is kind of what our job is right?). I'd much prefer the above than just 'it won't let me log in' - where there maybe context that I'd want.
I spend more time asking follow up questions (without being able to provide even a modicum of solution) in many cases, I try to couch my 'questions answering questions' reply with why I am asking (more typing and explaining) when users don't give me chapter and verse, even if it is mostly 'puff'.
> I now work as a software developer for a startup and often have to interact directly with clients, and when I communicate with them, I always make sure have my desired "call to action" (even if only summarised) within the first sentence.
But that is after they have emailed you right? You cannot summarize anything until you actually have them tell you what is wrong, no matter how long takes them. So yes summarize in the first sentence is always useful and if you don't kow the solution (yet) it never hurts to admit that and say something like, 'but we can try X or see what Y is doing as that will help me understand the issue in more detail' etc.
Customer Support is hard work sometimes, now try doing it with someone who doesn't speak your language very well ;)