When do we need curly braces around shell variables?

When do we need curly braces around shell variables?

bash shell syntax curly-braces

bash

What is the meaning of the ${0##...} syntax with variable, braces and hash character in bash?

bash variables syntax curly-braces

bash

bash functions: enclosing the body in braces vs. parentheses

bash function parentheses curly-braces

bash

Why bash4 expands curly braces differently?

bash shell rhel curly-braces expansion

bash