D>

D>type
D>TFirstCOMClass = class(TAutoObject, ICustomInterface1)
D>....

D>function TSecondCOMClass.CreateFirstCOMClass:ICustomInterface1;
D>var objFirstClass:TFirstCOMClass;
D>begin
D>  objFirstClass := TFirstCOMClass.Create; //корректно ли так делать ?
D>  Result := objFirstClass As ICustomInterface1;

D>//objFirstClass.Free - когда вызывать 
D>end;

function TSecondCOMClass.CreateFirstCOMClass:ICustomInterface1;
begin
  Result := TFirstCOMClass.Create as ICustomInterface1; 
  //objFirstClass.Free - когда вызывать  - никогда
end;