I just did this last night and it helped improve my game dramatically. I was being plagued with crowding at doorways into rabbitholes and other entryways, particularly when my Sim was in university but the problem is in home worlds as well. Sims would crowd around the doors waiting to get in then be late for work/school because they spent all day waiting for the other Sims to get inside first, making their performance drop, it was the worst! This overcrowding also slows down the entire game and is a big contributor to lag. If you're also having trouble with this, you've probably been told to just add more schools/workplaces to the world to solve the problem or to download some mods. Well Sims 3 doesn't run well with CC and mods and adding more rabbitholes is pretty ineffective in my experience. I ended up editing my Sims 3.ini file to lower the dynamic avoidance to 0.1 and since then, my game has been running at 98% (not quite 100% but really close). That might sound like a scary task but it's actually very fast and easy, you need no tech or coding knowledge whatsoever, you just need to be able to navigate your computer, read and follow instructions and copy/paste. Editing this file in this way will allow Sims to walk through each other to get places, largely improving routing and game lag. It does look quite silly at times but your game will run better. copied from NRaas' Tips and Tricks page here: http://nraas.wikispaces.com/Tips+and+Tricks+FAQ If your game is still slow and barely playable after doing this, I suggest getting rid of ALL your CC and mods except for Overwatch since Twallan's Overwatch cleans up your game and improves long-term performance. Sorry but Sims 3 just isn't well-equipped to handle CC and mods, it's better to do without them. Also, boost all your graphics settings to the highest possible setting, except for the number of lots that load at once. Keep that at 1. It's a very strange tip, I know, but for some unexplainable reason, it works and many people have reported smoother gameplay after maxing out their graphics settings, much to everyone's amazement.