See people don't take improvement exams by themselves obviously just if they fail they by default have to give it anyway. So of course if you are failing a subject, it's going to be a disgrace for sure and in further admission processes for junior colleges it will be mentioned that you've given the improvement exam. So as such there are no disadvantages, but it will be a stamp on your career. That's it otherwise don't think of improvement exam, give your level best in the initial original exam itself.
Thankyou. Best wishes.