@djsumdog
I usually do side-quests before finishing the main story, so in a way I strive for the completionist playthrough, but I don't go autistic about it. Like if I play Pokemon, and it would take tens of hours to maybe have a shot at catching a particular pokemon, I clearly won't actually do it, but otherwise I do try to catch everything.
It depends of course what you mean by "100%", but I rarely actually do 100%, because there are too many little things to do in games that would basically require to play with a couple of walkthrough guides opened on a separate screen (because otherwise you're likely to miss that you can find a special item in a special place if you do a special thing).