TikTok is a popular social media app made in China that makes it easy to share videos. As with a lot of tools and applications on the Internet that makes things easy, there could be some drawbacks to them whether it is security holes due to the convenience of use or processes that the app is doing behind the scenes that you don't know about it. This article from boredpanda discusses quite a few items that a reverse engineer found that the app does in the background. If you are interested in what he found give it a read at this link.
Guy Who Reverse-Engineered TikTok Reveals The Scary Things He Learned, Advises People To Stay Away From It