As a photographer I like to note the depth of certain features on a wreck to help plan future dives and decompression obligations. Sometimes I’ll run a reel between two common points and take a compass heading to use for future dives. I won’t likely remember them all unless I write them down. As someone else mentioned, my logs are more of a journal: What cool stuff I saw, ideas for future shoots, what I should add to my camping supplies, etc. I also write down where I was wearing my lead... I mostly dive steel 100 doubles and a drysuit and my trim is good unless I carry two deco bottles. Then I’m slightly head down unless I put a weight in each pocket on my drysuit. There are so many reasons to keep track of your dives.