bitcoin-qt “backup wallet” vs copying wallet.dat


I am new to bitcoin, I wander what are the differences, and pros/cons (if any) between the file generated by bitcoin-qt when clicking on “backup wallet” vs copying the file “wallet.dat”? I see these files are indeed different with “cmp” so I am assuming that there are differences between these files. Can one of these files recover all of the information in the other?

EDIT: after a few backups I noticed that if I close the wallet, and then wait a few minutes. A backup at this moment equals the wallet.dat file.