@Bessieboo I have managed to avoid the patch but many have repurchased their entire games from Steam to avoid it.
Basically, it means you need to play through Origin. It recommends you don't enable all of your expansions and stuff packs and you need to check a lot of boxes to enable the ones you do want to play with each time. Often it unchecks them again and you end up having to relaunch the game. If you open a save and don't have the expansions and stuff packs used in it enabled it will apparently corrupt the save. People generally seem to find it very frustrating and game breaking. There was nothing in it to fix any game related problems so all mods still work. Some mods that have the version number in them will pop up a message saying you have the wrong version but I think most, if not all, of them have got versions with the 1.69 version number available now.
Patch 1.69 is only for the PC version of the game launched through Origin. If your disk version of the base game was purchased before before September 2012 you ought to be able to avoid it if you install it without the EADM or Origin link. But if your base game is a later version, or is a digital version, then you'll find you need to patch to 1.69 unless you got it from Steam. That's why so many people have repurchased their entire games on disk through Steam when there are sales on.
Someone else who actually plays with the 1.69 patch will undoubtedly give you a better idea of what's right or wrong with it. I've just basically outlined the bits of it that I wanted to avoid.
EDIT: This thread might give you more insight.
https://forums.thesims.com/en_US/discussion/868889/update-to-sims-3-on-origin-caw#latest