Definitely never too late to start one!
I started a log this year since I'm exploring a lot of new territory (who'd a-thunk that the upper Willamette Valley streams are new to me even though I've lived in the Portland area for all of my 47 years?). Then I went one step further and started sticking pins in a map.
After a few trips, I've got a nice visual representation of where I've been and how well the trips worked out. One color of pin for "saw trout", one for "caught trout", one for "couldn't tell if trout live here", and one for "don't bother".