At least on here I only catalog my actual games, just because I like to keep track of how many I have and for what collections.
Once I reach the milestone of 2000 games which is looking to happen a lot sooner than I expected, I actually wanted to actually find the market value of my entire collection for the sake of insuring it. I also think it would be interesting/useful to know this in the event, god forbid, I ever had to sell my collection. I know the values on stuff goes up and down all the time, but I would like to at least capture how much it's worth at a recent point in time.