My save game started in Twinbrook and I used the change hometown feature of Traveler to move to Bridgeport, as per the instructions. Since settling into Bridgeport as a new homeworld, there is a new "Bridgeport_0x09ffe3d7ExportDB" file in my save folder.

Does this mean that I no longer require the Twinbrook ExportDB package, as long as I keep the Twinbrook nhd file? Can it be safely deleted?

I have 16 nhd files in one game for my 16 Traveler mod connected worlds, Accordingly, I also have 16 much smaller ExportDB files. Not sure if it's ever been explicitly defined what those files do, I think they may have to do with portability to other game saves should that ever be needed, but I'm pretty sure best practice is to leave them alone. They shouldn't be taking up much space or overhead, by comparison with other things.

ExportDB files contain outfits for Sims from the world it's named after. These are used on mini sims visiting the currently simulated world. You should not delete it unless you never intend on returning there and want all relationships/family members to be wiped in which case the NHD should be deleted too with both ErrorTrap and Overwatch installed.