Insane as I am, I am trying to register all my parts (give or take...). For the time being, I am nearly through the sets. Parts collected and registered, taken notes of missing or replaced bricks.
Once through the sets, I will count the loose parts (and sort those bricks that have not been that yet) - coming from different sources. I use Rebrickable for the parts. This way, I can see if I have other sets in the collection, that might be interesting enough to find the parts for. Eventually to sell sets from themes I have no interest in. I also will check up, if I have some parts to complete sets that miss some bricks.
Final aim is to find out how big the collection is. I have a rough estimate, though I would like to get closer to the actual number.
It takes a lot of time, no doubt about it. Sometimes breaks are longer that I would like them to be, but it can drive you crazy...