By using your powermeter and correlating it with your heart rate you can really gain some insight into your fitness and recovery.

The most important factor is that the power meter you use, is reliable and consistent day after day. Like many athletes I know, we often ride different bikes including a trainer throughout a week or training phase. The z2 heart method is just 1 way to detect variance among power meters without doing full on threshold testing on each bike or trainer. This simply gives you an estimate of significant differences between different powermeters.

From here you can determine the percentage difference, or a good estimate on how many watts difference there Is between power meters and give a guideline to creating zones based on specific bikes/ power meters.

Calculating your threshold from Z2 is not always accurate in that we may be aerobically fit but lack threshold endurance due to where we are in our training cycle. Use this method sparingly.

Using a power meter is just one tool that can give a lot of current and post ride feedback, but this tool becomes even more valuable when tied in with heart rate and perceived effort to really give good guidance and can show specific weaknesses and strengths.

With experience, you'll know your race power and your race heart for different intensities and durations. This is extremely valuable when you start your race and your power meter either does not work, or is not calibrated and giving wildly unusable power numbers. Because you've ridden so many miles, with so much power:heart rate data correlation, you'll be able to stay within your power zones by, (blindly) using your heart rate instead.

Lastly, the more you ride the more you know. Using power can help give you some analysis on your aerodynamics. A better bike fit, better aerodynamics, the faster you can go for the same or lower power.