I really disagree with this. I think it’s really unfair, and quite frankly bad practice, to attend a VS knowing you won’t accept a TC with the firm at the end. You’re literally taking up a space that could go to another person that would actually die for that TC.
If you’ve already been successful in securing a TC at Firm A, I don’t really understand the point of a) wasting Firm B’s time, as vacation schemes are primarily run with the aim of recruiting trainees and b) actively making the decision to take the opportunity away from someone else, knowing how few and far between VS places are. Just my two cents though