Even without thinking about overtraining, we need to be fresh enough to maximize our interval efforts. At the same time, taking time off to freshen oneself isn't helpful, either. It's a difficult balance. I do a bit of zone 3 training during base rides, like now, but that'll quit when I start preparing for the season, like March, because I'll start doing "low-intensity" intervals then. So that's kind of my rule: either ride some Z3 or ride intervals. Sometimes one's better, sometimes the other.