Depends what you want, a nice diary with pictures etc to read in your old age, nothing wrong with that, I wish I had done that as well as keeping a digital record. I found a digital record best done on excel. Headings and date, weather, air and water temps, barometer readings, moon phases, water colour, wind, venue, bait, species etc. They can all be digitalized and build up into a useful help. The good thing with excel you can sort into whatever criteria you want for whatever, species, venue, time of year, bait, wind direction, etc -whatever you want, no end to what you can do with it.
Something useful or something artistic, both have their merits. And the idea that it takes over from the pleasure from fishing is not right, sorry to disagree with some but I found it took about 15-20 mins per trip and never missed a bite while doing it! Made fishing very interesting as well as a pleasure and lots to play with on a wet winters day which resulted in a useful guide. I would do both now, no problem at all so dont be put off. To be honest I dont understand why everyone doesn't do this. You have one fishing life, why waste it, make the most of it.