Is the [Ref] attribute of a const record parameter useful?

Pretty much as described in the documentation. You would use [ref]if you have a reason to force passing parameters by reference. One example I can think of is interop. Suppose you are calling an API function defined as follows:

typedef struct {
    int foo;
} INFO;

int DoStuff(const INFO *lpInfo);

In Pascal, you might want to import it like this:

type
  TInfo = record
    foo: Integer;
  end;

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

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

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