Although runners are often reluctant to take breaks, most breaks are beneficial in terms of overall development. A break gives both the body and the mind some time to regroup from what might have been a pretty strenuous period of training and competition. The length and timing of a break depends on how hard your training has been and how many unplanned setbacks you've endured over the past year. In any case, I recommend a serious break of a few weeks from training at least once per year, and it might also be wise to take other shorter breaks at different times in the same year.