I know you are eagerly waiting to optimize some real code, but please let me stay for a little bit more on the theoretical side of the equation. I spent all that time talking about the behavior of built-in data types but I didn't say anything about how data is passed to methods. This, much shorter and more surprising section (you'll see!) will fix this. As I'll be talking about speeding up method calls, I'll also throw in a short discussion of method inlining, just for a good measure. But first, parameters!
In essence, Delphi knows two ways of passing parameters to a method (or procedure, or function, or anonymous method, it's all the same). Parameters can be passed by value or by reference.
The former makes a copy of the original value and passes that copy to a method. The code inside the method can then modify its copy however it wants and this won't change the original value.
The latter approach doesn't pass the value to the method but just an address...