No CC means no custom content. Custom content is any content that is not from EA or Maxis, the creators of The Sims. This can include clothes, hair, furniture, etc. that have been created by other players and downloaded from the internet.
Some players prefer to only use content that comes from EA and Maxis, as they feel it is of a higher quality and is more balanced. Others enjoy using custom content as it allows for more creativity and customization. There is no right or wrong answer, it simply comes down to personal preference.
If you choose to download and use custom content, be sure to only download from reputable sources. There are many sites that offer free custom content, but not all of them are safe. Always check reviews before downloading anything, and only download from sites that you trust.