I know that ${var} and $var does the same thing. I also know that you can use brace for advanced options like ${var:=word} or ${var#pattern}. It's also explained here. But I see in some bash scripts the use of braces in the simplest form : ${var} and sometimes I see only this notation $var. Is there any reason to prefer this syntax over the simple $var as it does the same thing ? Is it for portability ? Is it a coding style ? As a conscientious developer, which syntax I should use ? 
What is the best practice between using ${var} or $var?
bash
It is for the sake of clarity. As pointed out by arzyfex, there is a difference between ${foo}_bar and $foo_bar. Always use braces, and you will never make that mistake. Also note that you need the braces if you wish to refer to positional parameters with more than one digit, e.g. ${11}.