Taqiya - conditions and goals?

The term [taqiya](https://en.wikipedia.org/wiki/Taqiya#Sunni_Islam_view) is often flung about in an uninformed manner, suggesting that it is halal to lie to Non-Muslims about all manner of things, in particular about Islamic doctrine, in order to further the interests of the ummah. To my understanding that is not the case, I can't find any scholars saying that that's the case in that breadth. My impression is that taqiya is a pretty niche term with very limited applicability. What's easy to find are scholars that relate taqiya to being forced to recant Islam under duress, such as torture or threat to life or similar. I can't find any thorough description of the range, conditions, and goals of taqiya though. It's possible there's a big difference between Sunni and Shia fiqh here. **Question:** For what purposes, under which conditions, and to what extent do Islamic scholars consider it halal for a Muslim to lie about his beliefs and the doctrines of Islam under the term "taqiya"? There's a somewhat rudimentary answer regarding Shiism [here](https://islam.stackexchange.com/questions/16977/what-do-shias-mean-by-taqiyya) , but that doesn't really have a lot of info. The different schools of law might have important differences in how they deal with taqiya, so an answer from any school of law will be useful already.