Information should be self-contained in the post. If someone wants to play detective and believes something they find is relevant to clarifying the scope of the question, they should do so via comment on the question and the question should be edited if that information is confirmed and useful.
I've been pretty bad at this in the past. I've used a user's profile to determine their age and refine an answer, and used a user's past post to make assumptions about their current question. These were bad things, and I really shouldn't have done them. So take this from a reformed contributor who now recognizes his own folly.
I'm not all bad though, I also use the same power of investigation to warn users that they may not be as anonymous as they think when asking.
The Appeal of the Forbidden Fruit
Following someone's profile in to the rabbit hole is easy, and digs up all sorts of stuff. With the growing size of the SE network, I can determine whether you like games, what your religion is, what programming languages you use (or don't use), and probably even get a good guess at your age and geographic location even if not in your profile.
Sometimes it is really tempting to focus on the specific situation rather than the general question (guilty) because it's just a lot easier to focus on your strengths than to take the time to generalize your experience. So if you can grab someone's age or location from their profile and start talking about that time you were 22 years old and working in Monrovia, Liberia, it feels like you're offering super specific advice and doing good. And that is awesome.
But it Causes Problems Long-Term
There are several issues with assuming information based on detective work.
The information may disappear
Users detach accounts or delete them, so whatever trail of breadcrumbs you followed may not exist in a year.
The question may not refer to a current personal situation
There are plenty of people who ask questions for friends, or who ask questions based on past events or events they have seen elsewhere. By using the user's information, you may be misreading the situation entirely.
The question is no longer self-contained
People come to this site through search engines which look at the title, body, and tags of a question. Our Google Overlords have not yet found out how to spider through all interconnected information on a user and make those inferences. So when someone stumbles on to a question about taking advantage of a crisis to get better salary, and see a summary of the tech market and why you can do better, they will likely be a wee bit confused.
And confusion is bad.
Doing detective work is fine. It may help you understand the person asking better, and give you a better idea of how you want to answer. However, before hitting that Post Your Answer button including that information, post a comment on the question asking if the information is appropriate for that question. If it is, then it can be incorporated in to the question as an edit, and everything becomes self-contained and relevant again.
If someone is posting based on details they dug up about you, and you don't think it is relevant in that case, just leave them a brief comment like:
It looks like your answer is focusing on the software industry, but I think this is a situation that can be found in almost any industry, so I'm looking for a more general answer. I appreciate the information, but could you please  your question to make it industry agnostic?
Feel free to downvote it if it's not helpful because of the detail included.
Just remember that at the end of the day, your information is publicly available, and while it may hurt the quality of the site if questions and answers aren't self-contained, that doesn't mean these answers should be flagged unless they are abusive in some way. Feel free to downvote, but don't expect a lightning bolt to smite any user who uses the tools at their disposal to collect publicly available information on you.