user109551: 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.

user-1: Maybe its copying it safely in a way that you can re-use it without any issues.
Update and lock the wallet, preventing any file corruption caused by updates during the copy
Luke Dashjr mentioned one of the reasons here: https://github.com/bitcoin/bitcoin/pull/18219#issuecomment-595010266

109551: <p>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 &quot;backup wallet&quot; vs copying the file &quot;wallet.dat&quot;? I see these files are indeed different with &quot;cmp&quot; so I am assuming that there are differences between these files. Can one of these files recover all of the information in the other?</p>
<p>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.</p>
 -1: <p>Maybe its copying it safely in a way that you can re-use it without any issues.</p>
<p><a href="https://github.com/bitcoin/bitcoin/commit/c1e07423083cd2a7e3f2b28f69a573ea1837af4d" rel="nofollow noreferrer">Update and lock the wallet, preventing any file corruption caused by updates during the copy</a></p>
<p>Luke Dashjr mentioned one of the reasons here: <a href="https://github.com/bitcoin/bitcoin/pull/18219#issuecomment-595010266" rel="nofollow noreferrer">https://github.com/bitcoin/bitcoin/pull/18219#issuecomment-595010266</a></p>
