How important do you think it is to do this?
I can say personally that measuring my practice has been a key part of my learning. Lately I have been filling one out for both drums and guitar. If at times I feel that I am struggling or stuck I only have to look at my practice log to realise the amount of work that has come before reaching this point in time. It puts things in perspective.
Athletes measure their sprint times on the track, their BMI and a lot of other things in order to maximize their potential. As musicians, how many of you measure your practice?