I take it that's a bit different for Windows Mail as it doesn't use dbx files anymore, but emails are stored as single eml files.
Why it bothers me is that I use an backup utility that makes a copy of those folders filled with eml files and every time Windows Mail compresses the original messages I get a message there is a difference between the files on my backup and the ones in the Windows Mail folders.
Most of the time it is only the time-stamp that has changed and nothing more.
Which is annoying in itself, because it disrupts sorting by date.
But it also leaves me wondering about the use of this feature at all.

Thx mfletch for that eye-opening piece.

But surprisingly enough, and again as ironic as it seems, the compaction process itself has also been implicated in causing corruption. - (then why the heck would OE do it ?)

Do not cancel this compaction, nor use your computer until it is finished. - (yeah, tell me about it. I literally go out of the room when that compaction beast takes over my laptop)

For best results however, you should still compact all folders on a regular basis, such as weekly or bi-weekly. - (again, why the heck OE would do the compaction ?)