What you need to know for training purposes is your power output in real time. Your average power output for a given length of time may be interesting but it is useless.

If you have a powermeter than tells you your instanenous power output in real time, you can determine your training zones based on power. Then you plan a training program based on these zones. For example, today workout will be three 10 minute intervals at zone 4 or maybe 280 watts (ie. you watch your powermeter and put out 280 watts for the 10 min interval), etc, etc, etc..