The best reason to save all of those sales candidate assessments which you ran last year can be answered with a few letters: EEOC. That's right. It's especially true if you don't follow the sales hiring process to a "T", or worse, if you don't always follow the recommendations on the assessment. Let's say that you loved one candidate so much that you hired him despite the recommendation not to do so. Let's also supposed that he was white and under 40. Let's also suppose that there was another guy, very strong, recommended on the assessment, but you didn't hire him. What if he went to an employment attorney and claimed that you discriminated. You know you didn't, but he wants to use it against you. Turns out that he was a protected minority. In case you aren't up to date on this subject, a protected minority is anyone who is not white, is 40 or older, and is not male. In other words, most candidates are protected minorities!
You would have to prove that all candidates were assessed, not just some, so you'll need all of your results as proof. You would also have to prove that you used the assessments consistently. Of course, in this case, you didn't! If you don't hire a recommended female, that's fine. Unless, of course, you hire the 34 year-old white male who was not recommended, prompting the female to sue. You would be pretty deep into the brown stuff at that point.
Here's a reason to keep the evaluations you did on your existing sales force in each salesperson's employment file. Suppose you terminate a salesperson for non-performance and he claims that the firing was unlawful. Let's say that they charged that you required them to take a sales evaluation. While there is nothing wrong with having employees evaluated, unless you can prove that you evaluated everyone, the former employee could claim that he was singled out.
High-quality, role-specific, accurate evaluations are terrific. But if you don't use them in way that is consistent with how they were designed to be used, you could run into trouble.