Is the [Ref] attribute for const record parameters useful?

It's pretty much as described by the documentation. You'd use [ref] if you had a reason to enforce the argument to be passed by reference. One example that I can think of is for interop. Imagine you are calling an API function that is defined like this:

typedef struct {
    int foo;
} INFO;

int DoStuff(const INFO *lpInfo);

In Pascal you might wish to import it like this:

type
  TInfo = record
    foo: Integer;
  end;

function DoStuff(const Info: TInfo): Integer; cdecl; external libname;

But because TInfo is small, the compiler might choose to pass the structure by value. So you can annotate with [ref] to force the compiler to pass the parameter as a reference.

function DoStuff(const [ref] Info: TInfo): Integer; cdecl; external libname;