From version 5.4 files are added to the Trusted File list automatically if (when checked) their certificate says that they are signed by vendors in the trusted vendors list.
According to the devs this is to improve performance - checking that a file certificate is current and valid and has been issued by a trusted vendor takes time as it requires communication over the internet. Adding files to the TVL means this check does not have to be done every time the file runs. I’d guess it would also improve reliability - internet-based checks could time out possibly leading to files being falsely identified as unknown.
The list may also fill up with files, including temporary files, dropped by trusted installers. The temporary files can be purged using the purge button.
Adding all these files will not cause capacity problems - according to the devs the TVL can handle millions of files with no difficulty.
Thanks to: Egemen, Captainsticks, & Heffed, who contributed information to this FAQ