The classic idea is to periodize training: start with base, move into tempo work, then into LT work, then into VO2max work. It's classic because it works.

CTS has pushed the intervals-all-the-time idea because you do get results quicker, but as asgelle says, the results are not as good.

A third way has become popular: polarized training which I've been doing the past couple years. In polarized, one does either z2 work or z5 work, nothing in between, the z5 work being 10%-20% of total time. I periodize that too, by starting with only z2 work for a few weeks before I start adding in high end work. I do more like 10% high end, while elites do 20%. OTOH my focus is on longer rides in the 3-10 hour category rather than crits which are more the focus of CTS time-crunched programs. Polarized z5 has been found to work best with 4 reps of 8 minutes.