You'll get HR based training zones. You'll get power numbers that correlate with the HR numbers, but they will be of little use to you in any practical sense. With the HR zones you should be able to structure your workouts to ensure that you are really resting on on recovery or endurance rides. HR is a somewhat useful for threshold intervals, but it lags. A few 20 minute efforts on the same stretch of road should let you bracket the effort to the right zone.

It's not a useful as when you have a powermeter, but 5 yrs ago nobody had a powermeter and we all trained effectively with HR meters.