What are the benefits of training in zone 2 to build your aerobic engine and base fitness?

Winter training miles = summer smiles!

I know you're not the biggest fan of steady state or cruise intervals. I've been reading Joe Friels latest book.. "Your best Triathlon. Advanced Training for Serious Triathletes"

Potentially interesting excerpt for you:

Aerobic endurance page 21

Zone 2 heart rate power or pace is the intensity that builds aerobic endurance. Go higher than zone 2 and you start to develop anaerobic endurance systems . Go lower than this and you are not working hard enough to challenge the aerobic systems

By the end of the base period you should swim bike and run faster than you did at the start of the base period. Mark Allen (6x hawaii ironman world champs winner) used a heart rate as the upper limit of 155 bpm of his running intensity - that's his zone 2!

When he first started he was running an 8:15 per mile pace (5:09/ km). Within a year he was running 5:20 per min mile (3:20 per km) wow! at the same heart rate. He had become 35 per cent faster without working any harder.

I know he trained aerobically a lot, and very strictly in his base period, dropping 60 seconds at the same heart rate in 12 weeks. Interesting hey. Need to get this on the swim, bike and run.