Question: This is not a technical question. However as the FAQs say this place is about

> 
> people who love to create well-structured and beautifully typeset documents
> 
> 
> 

I take my shot.

I am often confused when which font family is more appropriate. Most people would suggest: "take what you like the most". But there are typographicaly reasons and I don't want to pick a font familty randomly.

I am looking for some good paper reasoning about the choice of font family, no luck so far. Are there good sources?

Answer: 
* presentations: sans-serif
* documents:
	+ up to one/two pages: sans-serif or serif
	+ more pages: always serif
	+ header/titles maybe in sans-serif
Serifs are used for traditional things, and with themes like "corporate" and "formal", and for books & novels, etc. I use Sans Serif when the themes are "modern", "fun", "Colourful" and "playful"