During base building, compare EF over time (months) for Z2 rides. Look at when decoupling occurs on long rides. Also compare similar intervals (eg SST) and what your avg HR is during them. So within 1 workout and from week to week.
I typically compare the workout to the last time I did it and look at the average HR and EF of each interval. I find it hard to compare similar, but still different workouts, as smaller changes induration or %FTP can make a difference.
Q: is there actually any actionable daily metrics? Isn’t it more per block/phase/season for deciding how to move forward?
Daily I watch more for subjective feelings like motivation, sleep, appetite, etc to understand if need to dial back (likely) or can go harder (unlikely)?
I use intervals.icu. It is just power divided by HR. So the more power you get per heart rate the better. If the power is the same it does not matter, but if you are comparing workouts at different power levels you need to normalize the HR data.
EF as a long term metric on a certain type (longer z2) rides. HRrc just sometimes to look at trends. Personally the only metric along EF I care is aerobic impact score in WKO and aerobic TiS (I am very surprised that no one else uses similar system) as this is gives me best correlation between training and improvement in the long term.
I love all metrics but I treat them more as a fun fact rather I like to study than actionable items in any way.