Trump's team says it will "submit names for background checks and security clearances," an agreement typically signed even before the election. The FBI historically vets each cabinet nominee and also handles security clearances, a process that could not begin until the agreement was made.
Trump and his allies have been openly critical of the FBI both on the campaign trail and since the election. Kash Patel, Trump's nominee to lead the organization, has been a crusader against the "deep state" since Trump's first term and has echoed Republican claims that Democrats have "weaponized" the FBI.
https://www.foxnews.com/politics/trump-transition-signs-agreement-fbi-background-checks
This is a tactical move. More exposure.