I agree with Smrobs. If it's a young horse, it could be beneficial. If it's an older horse who knows their job, then there is no need. They know their job and what is expected of them. If they spend a few months not doing work, they aren't going to forget. Hell, if you want an example, there's a video somewhere of Shining Spark doing a perfect sliding stop after not being ridden for 11 years or so.
The most that's going to happen is that the horse may lose muscle conditioning that they would have from doing work undersaddle, but that can be kept in control with lunging exercises.