First, a little history of "Full Disk Access." It simply did not exist until the release of macOS Mojave in 2018. Up to that time apps had unlimited access to your computer's files & folders and as the user you were never asked to make a decision to allow an app to access whatever folders & files it needed. Since that time Apple has gradually increased the degree of control that Full Disk Access represents.
Here is Apple's explanation:
Apple believes that users should have full transparency, consent, and control over what apps are doing with their data. In macOS 10.15 or later, this model is enforced by the system to help ensure that all apps have obtained user consent before accessing files in Documents, Downloads, Desktop, iCloud Drive, and network volumes.
Full Disk Access is that user consent & control process. It is a stricter security & privacy feature than what macOS had before. But it has also led to confusion among users because now you have to grant Full Disk Access whereas before you didn't need to do anything.
As long as you trust the app, granting Full Disk Access to it is fine. They key is ... do you trust the app and its developer?
BTW, legitimate apps make use of Full Disk Access to work with the disks, files & folders the app needs; they don't go poking around "all your sensitive information." That's what malware does.