This user is trying to make a big list of the common sense (began in 2009). Oh it has taken too long...
The real problem behind the "not for extensive discussions" thing is probably that some answers on some subsites tries to appear formal and complete, while in fact, nobody knows an ideal answer. It could be still understandable on Workspace, but obviously horrible on Parenting. Answers on some other websites that nobody ever wanted a discussion usually tries to appear informal to acknowledge that "this might not be the perfect answer, but hope it has helped you a bit". On the other hand, they are more permissive to personal opinions and duplicates, instead, as a result. Alternatively, they simply don't have a commenting feature, but visible downvotes, to acknowledge that this answer is not verified by many.
Code Golf
Q&A for programming puzzle enthusiasts and code golfers
Programming Language Design and Implementation
Q&A for designers and implementers of computer programming languages
Puzzling
Q&A for those who create, solve, and study puzzles
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems
Information Security
Q&A for information security professionals
Area 51
Q&A for proposing new sites in the Stack Exchange network
Stack Overflow
Q&A for professional and enthusiast programmers
Computer Science
Q&A for students, researchers and practitioners of computer science
Meta Stack Exchange
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Worldbuilding
Q&A for writers/artists using science, geography and culture to construct imaginary worlds and settings
Politics
Q&A for people interested in governments, policies, and political processes
Philosophy
Q&A for those interested in the study of the fundamental nature of knowledge, reality, and existence
Community Building
Q&A for community managers, administrators, and moderators
Super User
Q&A for computer enthusiasts and power users
User Experience
Q&A for user experience researchers and experts
Board & Card Games
Q&A for people who like playing board games, designing board games or modifying the rules of existing board games
Chinese Language
Q&A for students, teachers, and linguists wanting to discuss the finer points of the Chinese language
Law
Q&A for legal professionals, students, and others with experience or interest in law
Mathematics
Q&A for people studying math at any level and professionals in related fields
Open Source
Q&A for people organizing, marketing or licensing open source development projects
Software Engineering
Q&A for professionals, academics, and students working within the systems development life cycle
Arqade
Q&A for passionate videogamers on all platforms
Japanese Language
Q&A for students, teachers, and linguists wanting to discuss the finer points of the Japanese language
Artificial Intelligence
Q&A for people interested in conceptual questions about life and challenges in a world where "cognitive" functions can be mimicked in purely digital environment
Theoretical Computer Science
Q&A for theoretical computer scientists and researchers in related fields
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts
Lifehacks
Q&A for people looking to bypass life's everyday problems with simple tricks
Personal Finance & Money
Q&A for people who want to be financially literate
Server Fault
Q&A for system and network administrators
Writing
Q&A for the craft of professional writing, including fiction, non-fiction, technical, scholarly, and commercial writing
Economics
Q&A for those who study, teach, research and apply economics and econometrics
Android Enthusiasts
Q&A for enthusiasts and power users of the Android operating system
Role-playing Games
Q&A for gamemasters and players of tabletop, paper-and-pencil role-playing games
Cross Validated
Q&A for people interested in statistics, machine learning, data analysis, data mining, and data visualization
Home Improvement
Q&A for contractors and serious DIYers
Computer Graphics
Q&A for computer graphics researchers and programmers
Bitcoin
Q&A for Bitcoin users, developers, and enthusiasts
Database Administrators
Q&A for database professionals who wish to improve their database skills and learn from others in the community
Retrocomputing
Q&A for vintage-computer hobbyists interested in restoring, preserving, and using the classic computer and gaming systems of yesteryear
Quantum Computing
Q&A for engineers, scientists, programmers, and computing professionals interested in quantum computing
Computer Science Educators
Q&A for those involved in the field of teaching Computer Science
English Language Learners
Q&A for speakers of other languages learning English
Game Development
Q&A for professional and independent game developers
Travel
Q&A for road warriors and seasoned travelers
Data Science
Q&A for Data science professionals, Machine Learning specialists, and those interested in learning more about the field
Psychology & Neuroscience
Q&A for practitioners, researchers, and students in cognitive science, psychology, neuroscience, and psychiatry
Music: Practice & Theory
Q&A for musicians, students, and enthusiasts
Physics
Q&A for active researchers, academics and students of physics
Software Quality Assurance & Testing
Q&A for software quality control experts, automation engineers, and software testers
Linguistics
Q&A for professional linguists and others with an interest in linguistic research and theory
The Great Outdoors
Q&A for people who love being outdoors enjoying nature and wilderness, and learning about the required skills and equipment
MathOverflow
Q&A for professional mathematicians
Reverse Engineering
Q&A for researchers and developers who explore the principles of a system through analysis of its structure, function, and operation
Cryptography
Q&A for software developers, mathematicians and others interested in cryptography
Biology
Q&A for biology researchers, academics, and students
Anime & Manga
Q&A for anime and manga fans
Electrical Engineering
Q&A for electronics and electrical engineering professionals, students, and enthusiasts
Academia
Q&A for academics and those enrolled in higher education