Recently in comp.lang.tcl, Darren New says: ... "You need to learn the difference between $address and address, and where each is appropriate.", then goes on to explain when one should use $variable_name and when one should use variable_name - some Tcl commands wants the name of a variable, while most want the value of a variable.
Overinterpreting metacharacters: "" and {} are just for grouping - foo is "foo" is {foo}. Only at whitespaces and substitutions, they make a difference.