1. Mathematics:
If the candidate is at 3 times more places, naturally their chances of getting a job will roughly increase 3-fold.
2. Candidate Commitment:
By the candidate going to more interviews it shows that they are more committed to leaving, meaning they are more likely to prepare better and are more likely to accept if offered, both of which will enhance the value of your process.
3. Positional Good:
Clients will naturally be more interested in a candidate who is interviewing at their competition. It validates their positive opinion about the candidate and creates a level of intrigue.