Well, these are just my opinions, and I do use some CC and mods. All iterations of the game have had flaws, and all iterations used mods and CC. One luxury that modders and CC makers have over the Sims team is that they are usually modifying, not creating, code. Also, most people will cut them some slack if the CC tears, doesn’t fit some frames, etc. We hold Maxis to a higher standard, rightfully. A Maxis fix should work across multiple platforms, multiple gaming set ups, and take into account all packs, and not produce conflicts. A modders hot fix may not. You will find that any major update to game code will break mods and some CC. As for gameplay mods, they’ve always been a great way to customize our personal games without Maxis foisting those preferences on everyone else. It avoids the “I never wanted this in my game, OMG, it’s ruined” reactions. By leaving some gameplay to mods, we have increased customization to personal preferences.
Mods are usually safe. Some may not be updated and that can cause problems for your game, but most modders update with every patch or pack. Yes, there are mods out there that are not family friendly. Those that break the game’s Teen rating can’t be discussed here. If you use a lot of mods and cc it does require some maintenance. That’s why I keep mine down to just those I find essential to my style of play.
The modding section of this forum is a great place for information on mods and cc.