President Wilson and I have done extensive research on tapering the last several years (refer to, http://www.abcbodybuilding.com/taperindex.php
President and I are of the mindset that an athlete should never need to take time off, but rather, they should taper, and implement tapering regularly into their program. If this advise is followed, I do not believe time off will be neccesary. However, there has been one or two debates on here suggesting that there may be some efficacy to taking time off.
It may be argued that time off is good from a psychological perspective. But I feel that this is entirely dependent on the individual. Many athletes absolutely hate taking time off, because they fear it will hurt their gains. But this certainly does not apply to everyone, so that argument may have some validity. It does not, however, invalidate the argument that taking time off is suboptimal to performance, from purely a physiological standpoint.
Currently, I have been doing massive research on tapering. President and I recently submitted a completely up-to-date research article on tapering to a peer reviewed journal; I just did a 90 minute lecture on the topic in a Masters Seminar, and composed a 40 page paper for that as well.
One of the key topics I wanted to investigate, was the effects of taking time off on exercise induced physiological and performance adaptations.
I found an excellent review article by Mujika and Padilla (2000) that thoroughly examined this question. Here is a summary of their findings:
The effects of 1-4 weeks of time off on Training Induced Performance & Physiological Adaptations in Advanced Athletes and In-experienced participants
(Created by Wilson, G., 2007; Data from Mujika & Padilla, 2000).
And as can be seen in our articles on here, and hopefully in our peer reviewed publication in the near future, tapering has the opposite effect of increasing all of these measurements.
Here is the reference, as well as a reference to the effects of chronic time off.
MUJIKA, I., and S. PADILLA. Detraining: loss of training-induced physiological and performance adaptations. Part I: short term insufficient training stimulus. Sports Med. 30: 79-87. 2000.
MUJIKA, I., and S. PADILLA. Detraining, loss of training-induced physiological and performance adaptations. Part II, Long term insufficient training stimulus. Sports Medicine 30, 145-154. 2000.