Passing a TStringList as Var-Parameter does not make sense in this context. The underlying instance has to be created and destroyed from outside, so you can even pass it as Const-Parameter.
Right and makes sense, only i prefer this usage (const vs var) with classes to distinguish between functions/procedures that read-only against what might change the content, so yes it is just cosmetic, like with this case and that example, but will makes difference with multithreads usage, easier to notice and remember and that is it, where and when need thread synchronization.
Also: we only can dream of compiler and more advanced Delphi/Pascal language feature to detect and prevent internal changes coming form class internal implementation, that makes const and var more powerful, producing safer memory and logical handling.