I know some people that use them for only recovery rides.
I don't have any monitoring system, no speed/cadence/power/heart. I do a 5-10min warm-up, hit the pedals for 15 min at a rate that challenges me. Take a 5 min cool down/rest and then do 15min hard again and rest again. I go for 10 min medium paced, them sprint for 2 mins in my 50x11 gear at 90-110 rpm. This pushes me to my limits, and helps my riding, only takes an hour.