I have categorized discussions in 4 groups
When in the context of a religion, the main goal of a discussion is to reach an already given conclusion. Any valid arguments are discharted if they contradict the given conclusion.
This kind of discussion is often held by religious people such as evangelists (the software kind too) or sales people. It's also the favorite form for drunk people trying to argue that they are not drunk.
Religious discussions also occur if you are too specialized. If the only tool you know how to use is a hammer, you are bound to use a hammer to solve every problem.
These are discussions without a goal. That might sound useless, but it's not that bad at all. It's about questioning your own beliefs.
It's a mind opener. It's about challenging your ideas, getting the big picture.
The scientific discussion is about reducing the complexity of a domain. The conclusions might be inaccurate, but it should result in the optimal solution all things considered. Issues like feasibility and return of investment are handled in these discussions as well as risks. It should be noted that a conclusion concluded today, might me changed tomorrow. Scientific discussions embrace and accept change.
Law is about details. The more the merrier. When you reach the maximum amount of details any human can comprehend, you are about half way there. The downside is that often the big picture and reasoning is lost in the pursuit for details. Although the focus is on details, even the details are sometimes lost in discussions like that. The last man standing is the one with photographic memory and who can stay awake the longest. To succeed in this category I suggest that you give up on any social life and start nit picking on your surroundings. Although there can be a winner in such a discussion, the real looser is the common sense and productivity.
Law is a primal discussion form and we are trained to master it when we have arguments in kindergarten about what is right and wrong and which kid has more candy (milimeterdemokrati).
When it comes to software development, you might have these different discussions at different points of time on your project. The religious discussions occur in the beginning of a project, or when changes to the project occur. Although the religious debate has a high return in the short term, the long term might suffer.
As the philosophical discussion is about challenging your current beliefs, it's great for workshops or when a project is stuck in a dead end.
The scientific discussion is great for decision making on a project. What separates a decision derived from a scientific discussion from a religious discussion is the scope.
The lawful discussion comes into play on a software project when someone feels he's not treated right. The discussion often can't be resolved by the parties involved and a third party is then required.
Let the discussions begin!