One of the absolute worst projects after the fire was trying to create our contents list from memory of 1400 square feet plus a garage with who knows what in it. Our contents list was 50 pages of an Excel spreadsheet, and I'm pretty certain it was only 3/4 of our things.
If you want to know how hard it is to recreate your home in your mind, close your eyes right now, imagine the space, and then write down everything you think is in there, including the brand. Then take your list into that space and see how much you forgot. It's like that game where there are ten items that you have to remember, except multiplied exponentially... and done under duress.
It is unlikely that your home will burn down (or a tornado will level your house or a flood will come through taking everything downstream). But... it CAN happen, and it can happen to YOU.
Other than having a plan for your family, which is of the highest importance, creating a home inventory is probably the best thing to do before a disaster. And if you never need it, at least you know everything in your home!
I have struggled with wanting to create a new contents list because the old one was so emotionally taxing. But I know it's important, and I'm starting to work on it, one room at a time.
In doing research for some of the resources for the new website (which should be ready by August 1), I found this home inventory system. It's free. I just set up our house in it with each room and closet labeled. It even has categories of items so that you can add quickly. Honestly, I wish I could have used this right after the fire. It likely would have made the inventory list easier.