Often settings like this are enabled to prevent trolling, spamming, misunderstandings, and in the case of ECC...scamming. Private messages (conversations) are very hard, or probably impossible, for Staff to monitor (such as seeing edit history), so having that editing time-frame helps to prevent problems.

One main example I can see is someone sending a PM, the person replies agreeing to something (doesn't even have to be a trade/contract thing; it could be personal), and then the original sender edits the PM to be something completely different. Because Staff cannot monitor/moderate PMs, there could be pretty big problems.

Personally, I would rather PMs keep that five-minute edit time-frame. The only change that would otherwise make sense is the inability to edit a PM once it has been read.

 

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